MB-17118: cluster_run finds pluggable-ui config files
MB-17118: cluster_run finds pluggable-ui config files

cluster_run searches ../build/cluster_run_ui_plugins/ for files matching
pluggable-ui-*.cluster_run.json, and adds those to the ns_server
configuration parameter ui_plugins.

Change-Id: I020adea379520bd9813bca8b9aa7c1d2be1af7ca
Reviewed-on: http://review.couchbase.org/57940
Reviewed-by: Dave Finlay <7b10a9ed9f70e64c30b07607a671ae61c33f14c8@couchbase.com>
Tested-by: Dave Finlay <7b10a9ed9f70e64c30b07607a671ae61c33f14c8@couchbase.com>

ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server