Fix wheel installs: account for purelib & platlib.

[jsirois]

This fixes a further corner-case detecting --prefix installation
site-packages directories surfaced by Red Hat based OSes where
"purelib" and "platlib" installation directories differ (lib/ vs.
lib64/). We now simply check each site-packages directory found
under the installation --prefix for an installation RECORD and use
the first such one found. This is safe since we know
pip install --no-deps --prefix <dist> only installs one distribution
once.

Fixes #1866

[jsirois]

I manually tested this on ubuntu:20.04 and centos:7 images. They both worked, but the interesting case was CentOS:

$ tox -epackage
$ docker run --rm -it -v $PWD/dist:/dist centos:7
...
[root@1d8919788a1a /]# python3 /dist/pex PyYAML ansicolors -- -c 'import yaml; print(yaml.__file__); import colors; print(colors.__file__)'
/root/.pex/installed_wheels/98c4d36e99714e55cfbaaee6dd5badbc9a1ec339ebfc3b1f52e293aee6bb71a4/PyYAML-6.0-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl/yaml/__init__.py
/root/.pex/installed_wheels/00d2dde5a675579325902536738dd27e4fac1fd68f773fe36c21044eb559e187/ansicolors-1.1.8-py2.py3-none-any.whl/colors/__init__.py
[root@1d8919788a1a /]# ls -l /root/.pex/installed_wheels/98c4d36e99714e55cfbaaee6dd5badbc9a1ec339ebfc3b1f52e293aee6bb71a4/PyYAML-6.0-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl/.prefix/lib64/pythonX.Y/
total 0
[root@1d8919788a1a /]# ls -l /root/.pex/installed_wheels/00d2dde5a675579325902536738dd27e4fac1fd68f773fe36c21044eb559e187/ansicolors-1.1.8-py2.py3-none-any.whl/.prefix/lib/pythonX.Y/
total 0

Note that PyYAML was originally installed under .prefix/lib64/pythonX.Y/site-packages whereas ansicolors was under .prefix/lib/pythonX.Y/site-packages and Pex dealt with that variance correctly.

[Eric-Arellano]

Intricate. Thanks for the great comment

[jsirois]

Lovely, this doesn't work on Mac: https://github.com/pantsbuild/pex/runs/7520701726?check_suite_focus=true#step:7:1857

I'll need to trim down CI and start debugging.

[jsirois]

Alright, please take another look - the strategy has changed slightly.

I re-ran the docker manual checks, still good:

[root@c6e3ad5cc268 /]# python3 /dist/pex PyYAML ansicolors -- -c 'import yaml; print(yaml.__file__); import colors; print(colors.__file__)'
/root/.pex/installed_wheels/98c4d36e99714e55cfbaaee6dd5badbc9a1ec339ebfc3b1f52e293aee6bb71a4/PyYAML-6.0-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl/yaml/__init__.py
/root/.pex/installed_wheels/00d2dde5a675579325902536738dd27e4fac1fd68f773fe36c21044eb559e187/ansicolors-1.1.8-py2.py3-none-any.whl/colors/__init__.py
[root@c6e3ad5cc268 /]# tree /root/.pex/installed_wheels/98c4d36e99714e55cfbaaee6dd5badbc9a1ec339ebfc3b1f52e293aee6bb71a4/PyYAML-6.0-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl/.prefix/
/root/.pex/installed_wheels/98c4d36e99714e55cfbaaee6dd5badbc9a1ec339ebfc3b1f52e293aee6bb71a4/PyYAML-6.0-cp36-cp36m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl/.prefix/
`-- lib64
    `-- pythonX.Y

2 directories, 0 files
[root@c6e3ad5cc268 /]# tree /root/.pex/installed_wheels/00d2dde5a675579325902536738dd27e4fac1fd68f773fe36c21044eb559e187/ansicolors-1.1.8-py2.py3-none-any.whl/.prefix/                                                                      
/root/.pex/installed_wheels/00d2dde5a675579325902536738dd27e4fac1fd68f773fe36c21044eb559e187/ansicolors-1.1.8-py2.py3-none-any.whl/.prefix/
`-- lib
    `-- pythonX.Y

2 directories, 0 files
[root@c6e3ad5cc268 /]#