CMake - added runtest and lint targets

[akosiorek]

Added runtest and lint targets:

runtest:

• depends on caffe target (will invoke caffe build if it wasn't built earlier)
• builds tests, which have been excluded from the main build
• sets up gtest filters based on CPU/GPU mode
• runs tests with --gtest_shuffle

lint:

• runs cpp_lint.py on all source files and headers with the exclusion of generated *.pb.* files

[jeffdonahue]

Great, thanks! I hope to review this for dev merge soon.