mediaObject: Fix critical warning removing bus watchers.
mediaObject: Fix critical warning removing bus watchers.

Watchers in pipelines are set in post constructor callbacks wich are
called from factories. This patch fix tests to create objects by
using factories

Change-Id: I6cef5b0b8dc3ce65c4d76308e0dd0ec850e67cd2

TribeMedia/kms-core,Kurento/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,Kurento/kms-core,Kurento/kms-core,TribeMedia/kms-core,Kurento/kms-core,TribeMedia/kms-core,ESTOS/kms-core,TribeMedia/kms-core,ESTOS/kms-core,ESTOS/kms-core,shelsonjava/kms-core,ESTOS/kms-core