build breaks because guests install libraries with python3.5 but uses python 2.7

[Amrith Kumar]

Something appears to break and has led to guests failing this way:

Dec 15 20:48:03 m2 trove-guestagent[1751]: Traceback (most recent call last):
Dec 15 20:48:03 m2 trove-guestagent[1751]: File "/home/amrith/trove/contrib/trove-guestagent", line 31, in <module>
Dec 15 20:48:03 m2 trove-guestagent[1751]: from trove.cmd.guest import main
Dec 15 20:48:03 m2 trove-guestagent[1751]: File "/home/amrith/trove/trove/cmd/guest.py", line 21, in <module>
Dec 15 20:48:03 m2 trove-guestagent[1751]: from oslo_config import cfg as openstack_cfg
Dec 15 20:48:03 m2 trove-guestagent[1751]: ImportError: No module named oslo_config

amrith@m3:/$ pip --version
pip 9.0.1 from /usr/local/lib/python3.5/dist-packages (python 3.5)
amrith@m3:/$ python --version
Python 2.7.12
amrith@m3:/$ cd /usr/local/lib
amrith@m3:/usr/local/lib$ find . -name oslo_config
./python3.5/dist-packages/oslo_config
amrith@m3:/usr/local/lib$

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/411507
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=48f4fa52f9ebc2673ef8c559791a3c9355b15f07
Submitter: Jenkins
Branch: master

commit 48f4fa52f9ebc2673ef8c559791a3c9355b15f07
Author: Amrith Kumar <email address hidden>
Date: Fri Dec 16 06:13:15 2016 -0500

    Fix Gate: Force pip2 instead of pip

    Something appears to have caused the xenial guests to install all
    python libraries into python 3.5 directories and therefore the guest
    won't launch. This change forces pip2 and in theory should get around
    that.

    Moved Redis and PostgreSQL installs after the trove-dep ones.

    Change-Id: I3bbe3bafa7ea3e627272103ac16a38f6a32a8a06
    Partial-Bug: #1650382