Add more fixed ips

Go from 256 to 4096 fixed IP addresses.

The large ops test spins up 3 sets of instances then deletes them all at
the end. We are working on bumping the large-ops number up from 50 to
175, so we will need at least 525 fixed ip addresses.

Change-Id: Ie6cfd6e191ec873e577166e33e94b5996190a1c2
Add zeromq config

Although features.yaml have a feature entry for zeromq, there's no
config option for zeromq. So, even if you have a DEVSTACK_GATE_ZEROMQ=1
in your environment, it won't work.
This patch enable the use of DEVSTACK_GATE_ZEROMQ=1 to run devstack
with zeromq instead of rabbit or qpid.

Change-Id: I81075fe23bc9a751c05a3f777f7409d0104c979e
Merge "Add more fixed ips"
remove libvirt work around

libvirt in precise-updates now has the fix that we need (released
on March 20th), so we should no longer have to have a local work
around for it.

Change-Id: Id094a7e3e3004acd3d47b7fe34161ed2995e095b
Merge "Add zeromq config"
Merge "remove libvirt work around"