core: Introduce createFenceExecutor method

Introduces createFenceExecutor() method with fence action type as
a parameter, which will create FenceExecutor instance with specified
fence action type and other parameters with default values.

Change-Id: Id4630801fc7b6940caabb646c653ef10df3f63a4
Bug-Url: https://bugzilla.redhat.com/1090799
Signed-off-by: Martin Perina <mperina@redhat.com>