Fixed #1307677: Local provider network-bridge default respects container type
Merge pull request #1078 from dimitern/lp-1307677

Fixed #1307677: Local provider network-bridge default respects container type

If "network-bridge" is not specified in environments.yaml for
a local environment, but "container" is explicitly given, this
PR changes the local provider to choose the correct default
network bridge name ("lxcbr0" or "virbr0").

Live tested.