MB-8663 Use internalSettings to set xdcr parameters.

Instead of environment variables.

Change-Id: I6ba6f70708e68675a3ada062842f0c8a412b3cf8
Reviewed-on: http://review.couchbase.org/28211
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>