make external network type as 'local'

and remove it from bridge mappings.
Network, which is used as a source of Floating-IP
should not be associated with any external interface.
It's not needed since Grizzly release.

Partial-Bug: #1357298
Related-bug: #1272349
Closes-bug: #1260051
Change-Id: I62c7ebaa099c3580ddb68c2a8906e1cd2321ba58
Merge "make external network type as 'local'"