Rename requires files to standard names

From bug report:
Rename tools/pip-requires to requirements.txt and tools/test-requires
to test-requirements.txt. These are standard files and tools in the
general world are growing intelligence about them.

Change-Id: Ie0bdb4908f45e47db43e84cd0c5fdc5263c035f4
Fixes: Bug #1179008
Merge "Rename requires files to standard names"