add lower-constraints job

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

Create a lower-constraints.txt to be used to enforce the lower bounds
in those tests.

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

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

Fix the lower-bound for requests-mock, since 1.1.0 does not actually
work.

Change-Id: I8740a80c64e24c8339ee9b0992c2f81b1784e672
Depends-On: https://review.openstack.org/555034
Depends-On: https://review.openstack.org/555402
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

.zuul.yaml

@@ -230,6 +230,7 @@
         - shade-functional-devstack
         - shade-functional-devstack-magnum
         - shade-functional-devstack-python3
+        - openstack-tox-lower-constraints
     gate:
       jobs:
         - bifrost-integration-tinyipa
@@ -237,3 +238,4 @@
         - shade-ansible-functional-devstack
         - shade-functional-devstack
         - shade-functional-devstack-python3
+        - openstack-tox-lower-constraints

lower-constraints.txt

@@ -0,0 +1,43 @@
+appdirs==1.4.3
+certifi==2018.1.18
+chardet==3.0.4
+coverage==4.0
+decorator==4.2.1
+deprecation==2.0
+dogpile.cache==0.6.5
+extras==1.0.0
+fixtures==3.0.0
+future==0.16.0
+idna==2.6
+iso8601==0.1.12
+jmespath==0.9.3
+jsonpatch==1.21
+jsonpointer==2.0
+keystoneauth1==3.4.0
+linecache2==1.0.0
+mock==2.0.0
+mox3==0.20.0
+munch==2.2.0
+netifaces==0.10.6
+openstacksdk==0.11.2
+os-client-config==1.28.0
+os-service-types==1.2.0
+oslotest==3.2.0
+packaging==17.1
+pbr==2.0.0
+pyparsing==2.2.0
+python-mimeparse==1.6.0
+python-subunit==1.0.0
+PyYAML==3.12
+requests-mock==1.2.0
+requests==2.18.4
+requestsexceptions==1.4.0
+six==1.11.0
+stestr==1.0.0
+stevedore==1.28.0
+testrepository==0.0.18
+testscenarios==0.4
+testtools==2.2.0
+traceback2==1.4.0
+unittest2==1.1.0
+urllib3==1.22

tox.ini

@@ -92,3 +92,10 @@ ignore = H103,H306,H4
 show-source = True
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
+
+[testenv:lower-constraints]
+basepython = python3
+deps =
+  -c{toxinidir}/lower-constraints.txt
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt