Add missing Find-modules and dependencies for flake8

Add Find-modules for:

• pycodestyle
• pyflakes
• flake8

Add missing dependencies for pycodestyle and pyflakes to our own build of flake8. Since LCG_96b flake8 is also available in LCG. So once all relevant branches are using it, we could decide to drop our own build.

Fixes ATLINFR-3297

AE Build FAILURE
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #118]

Oh dear, so it fails with:

-- Found typing: /cvmfs/sft.cern.ch/lcg/releases/LCG_95/typing/3.6.6/x86_64-centos7-gcc8-opt/lib/python2.7/site-packages  
CMake Error at /cvmfs/atlas.cern.ch/repo/ATLASLocalRootBase/x86_64/Cmake/3.14.3/Linux-x86_64/share/cmake-3.14/Modules/FindPackageHandleStandardArgs.cmake:137 (message):
  Could NOT find pyflakes (missing: _PYFLAKES_PYTHON_PATH)

I am not entirely sure how we make this compatible with multiple LCG versions. The situation is:

1. If pyflakes, pycodestyle, etc. is available in LCG we need to declare a dependency on them in PyModules/CMakeLists.txt so they get installed in our own LCG area.
2. If pyflakes, pycodestyle, etc. is NOT available in LCG the pip install flake8 will simply build them as part of PyModules and they get installed via AthenaExternals.

Should I simply remove the REQUIRED from the find_package calls?

Yes. Stop using REQUIRED for modules that may or may not be available. And then decide how to install flake8 based on PYFLAKES_FOUND and similar variables.

added 1 commit

• 7e390681 - PyModules: Fix for optional LCG dependencies of flake8

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resolved all threads

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #120]

@akraszna thanks for all the comments. I have to say, I just blindly copied code from https://gitlab.cern.ch/atlas/atlasexternals/blob/master/Build/AtlasLCG/modules/Findgraphviz.cmake. But sounds like this wasn't the most optimal example to begin with. I'll try my best ;-)

Apparently I didn't update all modules quite correctly when I introduced the lcg_python_external_module(...) function. But at least some of them do use the feature that I'm promoting here. Like for instance:

https://gitlab.cern.ch/atlas/atlasexternals/blob/master/Build/AtlasLCG/modules/Findpyxml.cmake

But don't get me wrong, I'm definitely not blaming you...

added 1 commit

• f708e4d7 - PyModules: Fix for optional LCG dependencies of flake8

Compare with previous version

No worries, I think I implemented all your changes.

Btw, while doing so (and using cmake 3.15.5) I found that our Findpip module doesn't seem to be working with that version. But that's for another MR to sort out.

changed the description

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #123]

resolved all threads

mentioned in commit e4858947