Rename requires files to standard names.

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: I9c1356f22f6527be44b4b3f6a77012156ff1637b
Fixes: bug #1179008

tox.ini

@@ -7,8 +7,8 @@ setenv = VIRTUAL_ENV={envdir}
          LANGUAGE=en_US:en
          LC_ALL=C
 
-deps = -r{toxinidir}/tools/pip-requires
-       -r{toxinidir}/tools/test-requires
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/test-requirements.txt
 commands = python setup.py testr --testr-args="{posargs}"
 
 [testenv:pep8]