test_push was broken because something added a dependency in autotest's adb_host.py on PIL.

This leaked into chromeos-admin's test_push task

I hotfixed the issue by reverting a CL in the import stack that I had landed a while ago: https://chromium-review.googlesource.com/c/484627/

This is not a fix.
- That CL should be relanded.
- PIL depedency: We should add it to venv, since we now depend on it. (in chromeos-admin for now, in autotest serverside code forevermore).

There is a longer term bug to break the chromeos-admin --> autotest unversioned dependency problem.