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: I31fa9fb5e6b1e4656424b4a56f58b71903641875
Fixes: bug #1179008
diff --git a/tox.ini b/tox.ini
index 924e844..e31e43d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -51,13 +51,13 @@
 
 [testenv:venv]
 commands = {posargs}
-deps = -r{toxinidir}/tools/pip-requires
-       -r{toxinidir}/tools/test-requires
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/test-requirements.txt
 
 [testenv:pep8]
 commands = flake8
-deps = -r{toxinidir}/tools/pip-requires
-       -r{toxinidir}/tools/test-requires
+deps = -r{toxinidir}/requirements.txt
+       -r{toxinidir}/test-requirements.txt
 
 [hacking]
 local-check-factory = tempest.hacking.checks.factory