Set ERL_MAX_PORTS on Mac OS X in cluster_run.

Default ERL_MAX_PORTS seems to be 1024. Set it to the same value as
NOFILE limit.

Change-Id: Id4183524fde22c9abb9453ca08f192bc632e9b7b
Reviewed-on: http://review.couchbase.org/12906
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>

cluster_run

@@ -72,7 +72,8 @@ def os_specific(args, params):
         ## Also, we build stuff in kind of dumb ways, so fix the path.
         dypath = ("%(pwd)s/../install/lib/memcached:"
                   "%(pwd)s/../install/lib:/usr/local/lib") % {'pwd': os.getcwd()}
-        params['env'] = {"DYLD_LIBRARY_PATH": dypath}
+        params['env'] = {"DYLD_LIBRARY_PATH": dypath,
+                         "ERL_MAX_PORTS": "2048"}
         params['env'].update(os.environ)
 
 def start_cluster(num_nodes, start_index, host, extra_args):