engine: Introduce ParallelMultipleActionsRunner

The ParallelMultipleActionsRunner designed to execute
multiple actions in parallel. Since there is not boundary
to the number of parallel threads, it should be used wisely.

Change-Id: I03a381eb9e3e9d26aeba324fe568a16a44ecef80
Signed-off-by: Moti Asayag <masayag@redhat.com>