Pass contrail_extensions_enabled for DBInterface.__init__

In the vnc interface, while initializing the DBInterface for a non-auth
user, contrail_extenstions_enabled was missed out.

Change-Id: I3a40248345c29e6fa6d264c7e67ac5a44b45e89a
Merge "Pass contrail_extensions_enabled for DBInterface.__init__" into R2.0