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.

Fixes: bug #1179008

Change-Id: Iecf14056de51aed75f8ce46c6ef43f3167d7736d

tox.ini

@@ -9,8 +9,8 @@ setenv = VIRTUAL_ENV={envdir}
          NOSE_OPENSTACK_YELLOW=0.025
          NOSE_OPENSTACK_SHOW_ELAPSED=1
          NOSE_OPENSTACK_STDOUT=1
-deps = -r{toxinidir}/tools/pip-requires
-       -r{toxinidir}/tools/test-requires
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/test-requirements.txt
 commands = nosetests {posargs}
 
 [tox:jenkins]