Use python3 to calculate freezes

We need the integration gate to work with both trusty (python3.4) and
xenial (python3.5).  Rather than hard code the full python binary just
use python 3 and let the OS mange this for us. This is less than ideal
but it's the best we can do right now to unblock the gate.

We also address a short term issue with out upper-constraints.txt files
and manually copy the constraints from 3.4 to 3.5

Related-Bug: 1620436
Change-Id: I6acabf86933b7a7bce7baf44e6b512e7d0d2f6db

README.rst

@@ -154,7 +154,7 @@ generate-constraints
 Compile a constraints file showing the versions resulting from installing all
 of ``global-requirements.txt``::
 
-  generate-constraints -p /usr/bin/python2.7 -p /usr/bin/python3.4 \
+  generate-constraints -p /usr/bin/python2.7 -p /usr/bin/python3 \
     -b blacklist.txt -r global-requirements.txt > new-constraints.txt
 
 edit-constraints
@@ -185,12 +185,12 @@ Regenerating involves five steps.
 
 2) Create a reference file (do this without your patch applied)::
 
-    generate-constraints -p /usr/bin/python2.7 -p /usr/bin/python3.4 \
+    generate-constraints -p /usr/bin/python2.7 -p /usr/bin/python3 \
       -b blacklist.txt -r global-requirements.txt > baseline
 
 3) Apply your patch and generate a new reference file::
 
-    generate-constraints -p /usr/bin/python2.7 -p /usr/bin/python3.4 \
+    generate-constraints -p /usr/bin/python2.7 -p /usr/bin/python3 \
       -b blacklist.txt -r global-requirements.txt > updated
 
 4) Diff them::

openstack_requirements/cmds/generate.py

@@ -56,11 +56,11 @@ def _freeze(requirements, python):
     executables to test under, and then union the results. This is in fact the
     key difference between a constraints file and a requirements file: we're
     not triggering installation, so we can and will list packages that are
-    not relevant to e.g. Python3.4 in the constraints output.
+    not relevant to e.g. Python3 in the constraints output.
 
     :param requirements: The path to a requirements file to use when generating
         the constraints.
-    :param python: A Python binary to use. E.g. /usr/bin/python3.4
+    :param python: A Python binary to use. E.g. /usr/bin/python3
     :return: A tuple (python_version, list of (package, version)'s)
     """
     output = []
@@ -167,7 +167,7 @@ def main(argv=None, stdout=None):
     parser.add_option(
         "-p", dest="pythons", action="append",
         help="Specify Python versions to use when generating constraints."
-             "e.g. -p /usr/bin/python3.4")
+             "e.g. -p /usr/bin/python3")
     parser.add_option(
         "-r", dest="requirements", help="Requirements file to process.")
     parser.add_option(

tools/integration.sh

@@ -67,7 +67,7 @@ UPDATE="$tmpdir/all_requirements/bin/update-requirements"
 # Check that we can generate an upper-requirements.txt file with the change
 # that is being proposed.
 $tmpdir/all_requirements/bin/generate-constraints -p /usr/bin/python2.7 \
-    -p /usr/bin/python3.4 -b $REPODIR/requirements/blacklist.txt \
+    -p /usr/bin/python3 -b $REPODIR/requirements/blacklist.txt \
     -r $REPODIR/requirements/global-requirements.txt
 
 for PROJECT in $PROJECTS ; do

upper-constraints.txt

@@ -111,6 +111,7 @@ django-openstack-auth===2.4.0
 django-pyscss===2.0.2
 dnspython===1.14.0
 dnspython3===1.12.0;python_version=='3.4'
+dnspython3===1.12.0;python_version=='3.5'
 doc8===0.7.0
 docker-py===1.7.2
 docutils===0.12
@@ -230,6 +231,7 @@ oslotest===2.10.0
 osprofiler===1.4.0
 ovs===2.5.0;python_version=='2.7'
 ovs===2.6.0.dev3;python_version=='3.4'
+ovs===2.6.0.dev3;python_version=='3.5'
 packaging===16.7
 paramiko===2.0.2
 passlib===1.6.5