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.

Update the lower bound for PrettyTable so the unit tests pass.

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

Change-Id: Ia146248b505e66adf871d17ae1e4921d7888bb85
Depends-On: https://review.openstack.org/555034
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

.zuul.yaml

@@ -25,8 +25,10 @@
         - cliff-tox-py27-neutronclient-tip
         - osc-tox-unit-tips:
             branches: ^master$
+        - openstack-tox-lower-constraints
     gate:
       jobs:
         - cliff-tox-py27-neutronclient-tip
         - osc-tox-unit-tips:
             branches: ^master$
+        - openstack-tox-lower-constraints

lower-constraints.txt

@@ -0,0 +1,37 @@
+alabaster==0.7.10
+Babel==2.3.4
+bandit==1.1.0
+cmd2==0.8.0
+coverage==4.0
+docutils==0.11
+extras==1.0.0
+fixtures==3.0.0
+gitdb==0.6.4
+GitPython==1.0.1
+imagesize==0.7.1
+Jinja2==2.10
+linecache2==1.0.0
+MarkupSafe==1.0
+mock==2.0.0
+pbr==2.0.0
+prettytable==0.7.2
+Pygments==2.2.0
+pyparsing==2.1.0
+pyperclip==1.5.27
+python-mimeparse==1.6.0
+python-subunit==1.0.0
+pytz==2013.6
+PyYAML==3.12
+requests==2.14.2
+six==1.10.0
+smmap==0.9.0
+snowballstemmer==1.2.1
+Sphinx==1.6.2
+sphinxcontrib-websupport==1.0.1
+stevedore==1.20.0
+testrepository==0.0.18
+testscenarios==0.4
+testtools==2.2.0
+traceback2==1.4.0
+unicodecsv==0.8.0;python_version<'3.0'
+unittest2==1.1.0

requirements.txt

@@ -3,7 +3,7 @@
 # process, which may cause wedges in the gate later.
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
 cmd2>=0.8.0 # MIT
-PrettyTable<0.8,>=0.7.1 # BSD
+PrettyTable<0.8,>=0.7.2 # BSD
 pyparsing>=2.1.0 # MIT
 six>=1.10.0 # MIT
 stevedore>=1.20.0 # Apache-2.0

tox.ini

@@ -50,3 +50,10 @@ commands = {toxinidir}/integration-tests/openstackclient-tip.sh {envdir}
 [testenv:docs]
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -b html doc/source doc/build/html
+
+[testenv:lower-constraints]
+basepython = python3
+deps =
+  -c{toxinidir}/lower-constraints.txt
+  -r{toxinidir}/test-requirements.txt
+  -r{toxinidir}/requirements.txt