Fix/Cleanup nova.conf for quantum

Do not set network_manager when using quantum.  Addtionally stop creating
config values that are just needed for nova-network.  Support for nova-network
was dropped some time ago for this barclamp.

Set the correct vif Interface driver of when using quantum with linuxbridge.
Merge pull request #213 from rhafer/fix/nova-conf-cleanup

Fix nova.conf for quantum linuxbridge driver