Use an alias to boost::variant instead of wrapping the type

[MakersF]

This fails to compile. Yet have to figure why and how to fix.

In file included from /usr/include/boost/variant/variant.hpp:2412:0,
                 from /usr/include/boost/variant.hpp:17,
                 from resilient/include/resilient/detail/variant_boost2.hpp:7,
                 from resilient/include/resilient/common/variant.hpp:14,
                 from resilient/include/resilient/task/failable.hpp:6,
                 from resilient/include/resilient/task/task.hpp:28,
                 from resilient/test/task.t.cpp:1:
/usr/include/boost/variant/detail/variant_io.hpp: In instantiation of ‘void boost::detail::variant::printer<OStream>::operator()(const T&) const [with T = res
ilient::NoFailure; OStream = std::basic_ostream<char>]’:
/usr/include/boost/variant/variant.hpp:978:24:   required from ‘boost::detail::variant::invoke_visitor<Visitor>::result_type boost::detail::variant::invoke_vi
sitor<Visitor>::internal_visit(T&, int) [with T = const resilient::NoFailure; Visitor = boost::detail::variant::printer<std::basic_ostream<char> >; boost::det
ail::variant::invoke_visitor<Visitor>::result_type = void]’
/usr/include/boost/variant/detail/visitation_impl.hpp:114:9:   required from ‘typename Visitor::result_type boost::detail::variant::visitation_impl_invoke_imp
l(int, Visitor&, VoidPtrCV, T*, mpl_::true_) [with Visitor = boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char> >
 >; VoidPtrCV = const void*; T = resilient::NoFailure; typename Visitor::result_type = void; mpl_::true_ = mpl_::bool_<true>]’
/usr/include/boost/variant/detail/visitation_impl.hpp:154:41:   required from ‘typename Visitor::result_type boost::detail::variant::visitation_impl_invoke(in
t, Visitor&, VoidPtrCV, T*, NoBackupFlag, int) [with Visitor = boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char>
 > >; VoidPtrCV = const void*; T = resilient::NoFailure; NoBackupFlag = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>::has_fallback_type_; ty
pename Visitor::result_type = void]’
/usr/include/boost/variant/detail/visitation_impl.hpp:238:5:   required from ‘typename Visitor::result_type boost::detail::variant::visitation_impl(int, int, 
Visitor&, VoidPtrCV, mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = mpl_::int_<0>; step0 = boost::detail::variant::visitation_impl_step<boost::mpl:
:l_iter<boost::mpl::l_item<mpl_::long_<2l>, resilient::NoFailure, boost::mpl::l_item<mpl_::long_<1l>, {anonymous}::FailureMock, boost::mpl::l_end> > >, boost:
:mpl::l_iter<boost::mpl::l_end> >; Visitor = boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char> > >; VoidPtrCV = const void*; NoBackupFlag = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>::has_fallback_type_; typename Visitor::result_type = void; mpl_::false_ = mpl_::bool_<false>]’
/usr/include/boost/variant/variant.hpp:2318:48:   required from ‘static typename Visitor::result_type boost::variant<T0, TN>::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char> > >; VoidPtrCV = const void*; T0_ = resilient::NoFailure; TN = {{anonymous}::FailureMock}; typename Visitor::result_type = void]’
/usr/include/boost/variant/variant.hpp:2343:43:   required from ‘typename Visitor::result_type boost::variant<T0, TN>::internal_apply_visitor(Visitor&) const [with Visitor = boost::detail::variant::invoke_visitor<boost::detail::variant::printer<std::basic_ostream<char> > >; T0_ = resilient::NoFailure; TN = {{anonymous}::FailureMock}; typename Visitor::result_type = void]’
/usr/include/boost/variant/variant.hpp:2367:52:   required from ‘typename Visitor::result_type boost::variant<T0, TN>::apply_visitor(Visitor&) const [with Visitor = boost::detail::variant::printer<std::basic_ostream<char> >; T0_ = resilient::NoFailure; TN = {{anonymous}::FailureMock}; typename Visitor::result_type = void]’
/usr/include/boost/variant/detail/variant_io.hpp:88:5:   required from ‘std::basic_ostream<_CharT, _Traits>& boost::operator<<(std::basic_ostream<_CharT, _Tra
its>&, const boost::variant<U0, UN ...>&) [with E = char; T = std::char_traits<char>; U0 = resilient::NoFailure; UN = {{anonymous}::FailureMock}]’
/usr/include/gtest/gtest-printers.h:245:7:   required from ‘void testing_internal::DefaultPrintNonContainerTo(const T&, std::ostream*) [with T = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>; std::ostream = std::basic_ostream<char>]’
/usr/include/gtest/gtest-printers.h:338:49:   required from ‘void testing::internal::DefaultPrintTo(testing::internal::IsNotContainer, testing::internal::false_type, const T&, std::ostream*) [with T = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>; testing::internal::IsNotContainer = char; testing::internal::false_type = testing::internal::bool_constant<false>; std::ostream = std::basic_ostream<char>]’
/usr/include/gtest/gtest-printers.h:376:17:   required from ‘void testing::internal::PrintTo(const T&, std::ostream*) [with T = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>; std::ostream = std::basic_ostream<char>]’
/usr/include/gtest/gtest-printers.h:600:12:   required from ‘static void testing::internal::UniversalPrinter<T>::Print(const T&, std::ostream*) [with T = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>; std::ostream = std::basic_ostream<char>]’
/usr/include/gmock/gmock-spec-builders.h:1339:31:   required from ‘void testing::internal::ActionResultHolder<T>::PrintAsActionResult(std::ostream*) const [with T = boost::variant<resilient::NoFailure, {anonymous}::FailureMock>; std::ostream = std::basic_ostream<char>]’
/media/francesco/A6528DA1528D76B9/Programmazione/projects/resilient/test/task.t.cpp:80:1:   required from here
/usr/include/boost/variant/detail/variant_io.hpp:64:14: error: no match for ‘operator<<’ (operand types are ‘std::basic_ostream<char>’ and ‘const resilient::NoFailure’)
         out_ << operand;
         ~~~~~^~~~~~~~~~

[MakersF]

@amallia @SuperV1234 Suggestions?