Openstack image create command updates existing image (with same name) by
default. That might be confusing since glance allows create multiple
images with same names and may lead to unwanted image update by image
create command.
Image update code was moved from image create action to image set action.
BackwardsIncompatibleImpact
Change-Id: I1686c6544c366262efab9e33c066d5f8a667f707
Closes-Bug: #1461817