kmstestutils: fix warning disconnecting handler
kmstestutils: fix warning disconnecting handler

Change-Id: I418bed36b1b5d629319ba4ef057b37f1876d2bd5

TribeMedia/kms-core,ESTOS/kms-core,KurentoLegacy/gst-kurento-plugins,shelsonjava/kms-core,TribeMedia/kms-core,TribeMedia/kms-core,ESTOS/kms-core,KurentoLegacy/gst-kurento-plugins,TribeMedia/kms-core,Kurento/kms-core,KurentoLegacy/gst-kurento-plugins,ESTOS/kms-core,shelsonjava/kms-core,Kurento/kms-core,Kurento/kms-core,shelsonjava/kms-core,KurentoLegacy/gst-kurento-plugins,ESTOS/kms-core,Kurento/kms-core,shelsonjava/kms-core