Add options to set advertised addresses and ports

[sgotti]

When running behind a nat or another routable address (like docker with default bridge config) the listening addresses and ports will be different than the one the stolon processes are binded.
To handle this case some new --advertise options are needed.

Related to #101

[dddpaul]

Hi, are there plans to implement this new --advertise option?

[kainz]

so the docs/integration are poor, but I have this working via running stolon keeper --pg-listen-address/STKEEPER_PG_LISTEN_ADDRESS as your 'real' host address, and also setting these things to get the ports right:

PGPORT, STKEEPER_PG_PORT both to the external listening port, and also running with --pg-port with the same port number. This one was especially tricky IIRC because there was a bit of oddity in assigning the port number in the right places, and stolon-keeper was not owning setting all of them at the same time for me.