Force "use_vlan" to false on nova_fixed when using vlan modes

When ovs is used in vlan-mode quantums sets up an ovs-bridge to do the vlan
tagging. That bridge needs be attached to a none VLAN interface in order to
work correctly.

When linux-bridge is used quantum's linux bridge agent will create the correct
vlan interfaces automatically.
Merge pull request #217 from rhafer/fix/ovs-vlan

https://github.com/crowbar/barclamp-nova/pull/217

Merged by devtool for ArkadyKanevsky