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: Ic220b54de5ce7c15f442b8ffcb97cd03c2344f9a
Fixes: bug #1179008

tox.ini

@@ -9,8 +9,8 @@ setenv = VIRTUAL_ENV={envdir}
          OS_STDOUT_NOCAPTURE=False
          OS_STDERR_NOCAPTURE=False
 
-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]