Rename tools/pip-requires to requirements.txt

(and tools/test-requires to test-requirements.txt).

Requested by infra: bug 1179008

Change-Id: I7a6375622d095a9eda232ed82d167fc3a198ed06

tox.ini

@@ -2,18 +2,16 @@
 envlist = py26,py27,pep8
 
 [testenv]
-sitepackages = True
 setenv = VIRTUAL_ENV={envdir}
          LANG=en_US.UTF-8
          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}'
 
 [tox:jenkins]
-sitepackages = True
 downloadcache = ~/cache/pip
 
 [testenv:pep8]