Travis update

[jburel]

What this PR does

Use trusty to build
This is necessary to build with newer version of pytables
and newer version of ice

• building using ant fails all the time, need to use ./build.py.
• installation of python dependencies needs to be explicitly done via
  sudo apt-get during before_install: otherwise the dependencies will not be available to the container. This means that the python tests will fail with for example No module Ice. Change sudo option to required. I did not notice an increase in the build time with that change. See Issue with the Python path in the recent builds travis-ci/travis-ci#8048
• update numexpr via pip to avoid some table test failure e.g.
  test/unit/tablestest/test_servants.py:349: will fail with ValueError: Using `oa_ndim == 0` when `op_axes` is NULL. Use `oa_ndim == -1` or the MultiNew iterator for NumPy <1.8 compatibility

Testing this PR

Check that travis is green

See https://trello.com/c/gVsUkLH8/100-travis-upgrade

[rleigh-codelibre]

Looks generally OK.

I'm uncertain that sudo is required. Every package you are installing is in the trusty whitelist (https://github.com/travis-ci/apt-package-whitelist) because I requested them months ago and they have been available for a while now.

Did you find what build.py is doing which makes a difference? It's not related to sudo builds being run on different VMs?

[jburel]

without sudo: required it is not possible to install the python dependencies in before_install step.
When travis-ci/travis-ci#8048 is resolved we will probably have to revisit. Note that using group:edge as suggested in issue did not work

[jburel]

@rleigh-codelibre works now with ant. Still unclear why it was not before (without explicit error it is tricky to figure error)

[jburel]

@sbesson comment added to this PR too

[jburel]

--rebased-to #5447