7. core : Change AddVmTemplateCommand

This patch changes AddVmTemplateCommand and its child
CreateImageTemplateCommand to persist all async task placeholders
before executing the command on vdsm

http://www.ovirt.org/Features/AsyncTaskManagerChanges_3.3
Change-Id: I2d61e6b2a0f7967bcee463ff2384cb6daba892b9
Signed-off-by: Ravi Nori <rnori@redhat.com>