Check for MediaStreamTrack.stop() method previously to exec it
Check for MediaStreamTrack.stop() method previously to exec it

Change-Id: I0a52b7a0c8f0e10375f8feeb5b56c59b105bfd84

shelsonjava/kurento-utils-js,Kurento/kurento-utils-js,lcamacho/kurento-utils-js,Kurento/kurento-utils-js,Kurento/kurento-utils-js,shelsonjava/kurento-utils-js,lcamacho/kurento-utils-js