L3 Agent can handle many external networks

With this patch a l3 agent can handle
any networks by setting the neutron
parameter external_network_bridge
and gateway_external_network_id to
empty.

Related-Bug: #1234750
Related-Bug: #1194350

Change-Id: Id260a239df23951da730513f40cda490002effc3
Make timeout for ovs-vsctl configurable

This patch adds a new configuration variable for the timeout on
ovs-vsctl commands, and sets the default timeout to 10 seconds.
This is aimed at allowing users to tune the agents in order to avoid
timeout errors on their deployments.

Change-Id: I73ea0d0de49a4b4a118bc2d68ad9c093ea122717
Closes-Bug: #1254520
Merge "Make timeout for ovs-vsctl configurable"
Merge "L3 Agent can handle many external networks"