Allow seriesly host to be different to cbmonitor

Add seperate config options for the seriesly host, to allow seriesly
and cbmonitor to run on different machines.

(Added to allow local testing of perfrunner).

Change-Id: I2eb649a5b6b95177d50d9e3702f40a9827807228
Reviewed-on: http://review.couchbase.org/38003
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: buildbot <build@couchbase.com>