base

common_time: Move default election config to bcast.

cherry pick from I8ada3541cceca2e76c7a0c1a624a72026122c312

> common_time: Move default election config to bcast.

> Change the default master election and arbiration to use broadcast
> instead of multicast.  As nice as the idea of using multicast for
> discovery is, in the end it had just proven to be too unreliable in
> random people's home infrastructures as well as the more complicated
> managed infrastructures we are using internally.  Multicast still
> works, and the service can still be configured to use it, but for now
> we are switching to broadcast.

> Also, add runtime checks to filter out our own broadcast traffic as
> there does not seem to be any good sockopt in linux to do this for us
> (there is one for multicast, but not broadcast).

Change-Id: I0a7d0be4841d04bc03dcd8d49a4afa118797546d