engine: Add AddVmTemplateCommand to command executer framework

By adding AddVmTemplateCommand we can determine whether we need to delete
the template if the command failed.

Bug-Url: https://bugzilla.redhat.com/1105211
Change-Id: Ib47982264f535dcf38cd4f9319f842d75ebccd5d
Signed-off-by: Shahar Havivi <shaharh@redhat.com>