Update tox.ini to support RHEL 6.x.

In order to support running unit tests on RHEL 6.x we need to patch
eventlet with contrib/redhat-eventlet.patch. We already
have support for this in the tools/install_venv_common.py but we
need to make a couple changes to allow tox to consume this:

1) Sync in the latest intall_venv_common.py from oslo. This changes
 patch to use the -N option (ignore already applied patches) and
 makes it safe to call the patching function more than once.

2) Add a new patch_tox_venv.py script in tools.

3) Update tox.ini to call patch_tox_venv.py before it runs tests and
 coverage.

NOTE: This will hopefully go away eventually once this patch lands:

 https://bitbucket.org/eventlet/eventlet/issue/89/add-a-timeout-argument-to-subprocesspopen#comment-3342969

Change-Id: I3e2b07c3f718e4aede5c5f231ff0cdb7721ec885
missing - in --config-file

Fixes bug 1153374

Change-Id: I6ec9ee3e074a37fb550f8527b44db906136d78f9
Imported Translations from Transifex

Change-Id: I4ab820d1465af7b33a1e68217ad66f1594de39fa
Fixes Hyper-V agent issue with mixed network types

Fixes bug: 1153274

Due to a bug in setting up external ports the Hyper-V agent fails to work in
scenarios with VLAN and flat networks.

Furthermore, a warning message on Hyper-V 2012 indicates that external
port settings are ignored. As a result the agent can be simplified by
avoiding vswitch external ports configurations.

Change-Id: I860d22f427cb10dbeac422c1db2b3bcf9e84150f
Merge "Fixes Hyper-V agent issue with mixed network types"
Merge "Imported Translations from Transifex"
Merge "missing - in --config-file"
Merge "Update tox.ini to support RHEL 6.x."
Solve branch in migration path

Bug #1153578

Also, change a comment line in another migration where the 'revises' line
was incosistent with the id of the actual down_revision

Change-Id: I8effd70ba553330f9023605a2bfa92bd3d73bd4e
Sets default MySql engine to InnoDB

Fixes bug 1153594

Change-Id: I4a3de87a99ca2d49b6a74d7104daf47f8f421a80
Merge "Solve branch in migration path"
Imported Translations from Transifex

Change-Id: Ibd8c4ae41892acf2dba87869ac0ab28f4515ba60
Parallelize quantum unit testing:

This change switches run_tests.sh to use testr
in parallel mode, instead of nosetests, in order
to enable unit tests to run in parallel.

By default, the number of parallel test processes
is set to the number of cores on the test machine.

A similar change was recently merged to nova:
  https://review.openstack.org/#/c/15078/

Some tests required updating to remove inter-testcase
dependencies.

bug #1099694

Change-Id: Idfb923d424342a07dcba88d70b971683f549f763