Testing jobs must be correctly flagged to be skipped when mirrornet conversion...

Testing jobs must be correctly flagged to be skipped when mirrornet conversion pipeline is requested to avoid its failure. Also slightly changed logic used to perform optional actions specific i.e. to master/develop branches: instead of using conditional jobs, declared as manual and also having specified allow_failure=true, new conditional jobs just triggers child pipeline containing all unconditional manual jobs. In this case specifying allow_failure is not needed to make such job execution optional.