Update upper-constraints consumption

In order to deal with neutron going into the upper-constraints file so
that neutron plugins can consume it normally, we need to align the
constraints invocation in neutron's tox.ini. This means putting the -C
argument into the dependencies list rather than the pip install line so
that it doesn't get appended to tox installing neutron itself.

Needed-By: https://review.openstack.org/550475
Change-Id: I014177c8afcadd3e6acb20bd38bb9d9fcc778ed6

tox.ini

@@ -9,9 +9,11 @@ setenv = VIRTUAL_ENV={envdir}
 passenv = TRACE_FAILONLY GENERATE_HASHES http_proxy HTTP_PROXY https_proxy HTTPS_PROXY no_proxy NO_PROXY
 usedevelop = True
 install_command =
-    pip install -U -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+  pip install {opts} {packages}
+deps =
+  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -r{toxinidir}/requirements.txt
+  -r{toxinidir}/test-requirements.txt
 whitelist_externals = sh
 commands =
   {toxinidir}/tools/ostestr_compat_shim.sh {posargs}