workflows: exception handling improvement

• Removes any existing error messages that are displayed in Holding Pen when a workflow is continued to avoid causing the users to believe the error message is still relevant.

• Simplifies the exception handling when running workflows.

• Removes some duplicated logging.

Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>