MB-16435: OS X: Add correct rpath for vbuckettool & vbucketkeygen
MB-16435: OS X: Add correct rpath for vbuckettool & vbucketkeygen

Add explicit runtime linker search paths to vbuckettool &
vbucketkeygen so they can locate their runtime library dependancies
without an external DYLD_LIBRARY_PATH being set (which is no longer
possible from OS X 10.11 "El Capitan" onwards).

Change-Id: I74bdaa24cad5d09fd6653ccca1e7278d29f8536b
Reviewed-on: http://review.couchbase.org/55759
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

couchbase/moxi,membase/moxi,membase/moxi,couchbase/moxi,membase/moxi,couchbase/moxi,membase/moxi,couchbase/moxi,couchbase/moxi,couchbase/moxi,membase/moxi,membase/moxi