Provide way to pass rxtx factor to quantum

This patch adds a config option quantum_extension_sync_interval which by
default is set to 600 seconds. After 600 seconds the next time nova needs to
create a resource in quantum it will requery quantum for the extensions
that it has loaded.

Hopefully in Havana something smarter will be implemented rather than using
time sync. I believe a better way to implement this would be to have each
compute host keep a pool of persistant sockets open to quantum for it to
communicate over. Resync'ing then would only happen if the connection to
quantum broke because quantum needs to be restarted in order to change the
extensions it is using

Implemenets blueprint pass-rxtx-factor-to-quantum

Change-Id: I001cfaf348a3f0c8144c0226559752555c486db0
Merge "Provide way to pass rxtx factor to quantum"