add lower-constraints job

Create a tox environment for running the unit tests against the lower
bounds of the dependencies.

Add openstack-tox-lower-constraints job to the zuul configuration.

The nova-powervm project uses Nova's lower-constraints.txt file; it
doesn't need its own.

See http://lists.openstack.org/pipermail/openstack-dev/2018-March/128352.html
for more details.

Change-Id: I637abb9624bf237ef2e1e70bf40bb1d64e77d354
Depends-On: https://review.openstack.org/555034
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

.zuul.yaml

@@ -0,0 +1,7 @@
+- project:
+    check:
+      jobs:
+        - openstack-tox-lower-constraints
+    gate:
+      jobs:
+        - openstack-tox-lower-constraints

test-requirements.txt

@@ -7,7 +7,7 @@ coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 python-subunit>=1.0.0 # Apache-2.0/BSD
 python-swiftclient>=3.2.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.5 # BSD
 oslosphinx>=4.7.0 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0
 os-testr>=1.0.0 # Apache-2.0

tox.ini

@@ -12,8 +12,8 @@ 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
-       -egit+https://github.com/openstack/nova#egg=nova
-       -rhttps://raw.githubusercontent.com/openstack/nova/master/test-requirements.txt
+       -egit+https://git.openstack.org/openstack/nova#egg=nova
+       -rhttps://git.openstack.org/cgit/openstack/nova/plain/test-requirements.txt
 whitelist_externals = bash
 commands = bash tools/pretty_tox.sh '{posargs}'
 
@@ -42,3 +42,13 @@ exclude =  .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build,t
 
 [hacking]
 local-check-factory = nova_powervm.hacking.checks.factory
+
+[testenv:lower-constraints]
+basepython = python3
+deps =
+  # We just use nova's lower-constraints.
+  -chttps://git.openstack.org/cgit/openstack/nova/plain/lower-constraints.txt
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt
+  -egit+https://git.openstack.org/openstack/nova#egg=nova
+  -rhttps://git.openstack.org/cgit/openstack/nova/plain/test-requirements.txt