Fix missing libffi-devel for python-glanceclient

python-glanceclient is failing to install on rhel6 with a dependency
chain from pip as

  cryptography>=0.2.1 (from pyOpenSSL>=0.11->python-glanceclient==0.12.0.56.gb8a850c)

cryptography requires libffi-devel to build.  I'm not sure what
changed, but remove it from "testonly" so it is always installed.

However, RHEL6 includes this in the optional repo, so we enable this
repo in the fixup script.

Change-Id: I9da0e91b75f41578861ee9685b8c7e91dd12dae7
Merge "Fix missing libffi-devel for python-glanceclient"
Merge branch 'master' of github.com:openstack-dev/devstack