empty snapshot selector before adding new options
empty snapshot selector before adding new options

Change-Id: I9c48d7cf62f269c0ba2cd15f5c0ee0081cf9ec78
Reviewed-on: http://review.couchbase.org/25055
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Pavel Paulau <dd88eded64e90046a680e3a6c0828ceb8fe8a0e7@gmail.com>

couchbase/cbmonitor,mikewied/cbagent,couchbase/cbmonitor,pavel-paulau/cbagent,couchbase/cbagent,vmx/cbagent