Added CNHOST and CNBUCKET environment variables.

Updated test harness so host and bucket name can be passed
via environmental variables.

Change-Id: I0f2ff103447b955e5e24828ee97dd4521fbcaef8
Reviewed-on: http://review.couchbase.org/30042
Tested-by: Brett Lawson <brett19@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>