Use common db model class from Oslo
Use common db model class from Oslo

Modified common model class - added common `models.ModelBase` and
`models.TimestampMixin` classes as base class instead of object.
Renamed base model class from `ModelBase` to `GlanceBase`.
Removed duplicated code.

blueprint db-use-oslo-common-code

Change-Id: I6038adcfcb6b985736ac8d9374ac0a2fe1cdcc96

redhat-openstack/glance,dims/glance,redhat-openstack/glance,wkoathp/glance,vuntz/glance,wkoathp/glance,tanglei528/glance,openstack/glance,takeshineshiro/glance,jumpstarter-io/glance,jumpstarter-io/glance,dims/glance,akash1808/glance,saeki-masaki/glance,JioCloud/glance,stevelle/glance,rajalokan/glance,sigmavirus24/glance,kfwang/Glance-OVA-OVF,sigmavirus24/glance,klmitch/glance,paramite/glance,darren-wang/gl,openstack/glance,scripnichenko/glance,rajalokan/glance,ozamiatin/glance,kfwang/Glance-OVA-OVF,saeki-masaki/glance,akash1808/glance,ozamiatin/glance,paramite/glance,darren-wang/gl,tanglei528/glance,scripnichenko/glance,JioCloud/glance,takeshineshiro/glance,vuntz/glance,openstack/glance,klmitch/glance,stevelle/glance