Fix requirements gate + add local tox profile

Add a local tox profile 'requirements' so we can easily run requirements
checks locally during development.

Change-Id: I4d1718b6ff67a889984d8937241d086f06bef237

doc/requirements.txt

@@ -18,4 +18,4 @@ reno>=2.5.0 # Apache-2.0
 # This needs to be installed after above modules
 pydotplus>=2.0.2 # MIT License
 pyparsing>=2.1.0 # MIT
-networkx<2.0,>=1.10 # BSD
+networkx>=1.10 # BSD

tox.ini

@@ -184,3 +184,10 @@ whitelist_externals = sh
 commands =
     sh -c 'OS_TEST_PATH={toxinidir}/octavia/tests/unit stestr run {posargs}'
     sh -c 'OS_TEST_PATH={toxinidir}/octavia/tests/functional stestr run {posargs}'
+
+[testenv:requirements]
+deps =
+  -egit+https://git.openstack.org/openstack/requirements#egg=openstack-requirements
+whitelist_externals = sh
+commands =
+    sh -c '{envdir}/src/openstack-requirements/playbooks/files/project-requirements-change.py --req {envdir}/src/openstack-requirements --local {toxinidir} master'