Add third-party support for Quantum NVP plugin

This patch leverages the third-party mechanism provided by DevStack
to customize the configuration of DevStack instances when working
with the Quantum NVP plugin. This is useful in dev/test scenarios,
where connectivity between the DevStack VM and the NVP Gateway is
required.

Supports blueprint nvp-third-party-support

Change-Id: I3f5afa5de1219f491e37c8b9b28370855d6b017c
Add Fake virt driver support

nova fake virt driver can be used to simulate running arbitrarily large
number of VMs.  When the fake virt driver is selected, all other arbitrary
limits are disabled (quotas, scheduler limitations) as well. The fake
virt driver can be selected by adding the following line to your localrc

      VIRT_DRIVER=fake

This setting can be used to do simulated large scale (as defined by
number of VMs) testing (such as boot 500 VMs at once) inside a single
devstack instance.

Change-Id: I000c3cba107cd91bef11c4d5325e1ce7308faa6c
Merge "Add third-party support for Quantum NVP plugin"
Merge "Add Fake virt driver support"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp