engine, webadmin: synchronous multiple action

- Added a 'synchronous' version of run multiple actions to allow
  the frontend combine multiple single actions into one request and
  wait for the result of all of them. At the same time not disturb
  existing multiple actions that do NOT wait for the results.

Change-Id: I935f4257e731de719540db9d79d5865537be228d
Signed-off-by: Alexander Wels <awels@redhat.com>