casperjs tests for server groups

Change-Id: I2159747183013be1869a9b6e36284470a22a6194
Reviewed-on: http://review.couchbase.org/30024
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>