add couch_index_merger/ebin to test ebin path, so couch_skew can
add couch_index_merger/ebin to test ebin path, so couch_skew can

...be used in tests

Change-Id: I304a16bca078b0b305418ca323c1677aec583a16
Reviewed-on: http://review.couchbase.org/78339
Tested-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

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