make "zun pull" support Glance uuid

Current progress of "zun pull" does not support image uuid of glance. The bp is to make "zun pull" support uuid.
When use uuid to pull image from glance, some rules should be noted:
  When we pull image from glance, we can use image uuid, repo and repo:tag.
 If we use the the glance image uuid to pull image, we can always get the image as
long as the image exists in glance.
    If the tag of glance image is different from the docker image, we can get the docker image's tag and give a warning. In addition, we record the docker image's tag into db.