Specify the MetadefNamespace.namespace column is not nullable
Specify the MetadefNamespace.namespace column is not nullable

The metadef_namespaces table definition indicates the namespace
column as not accepting nulls. The related MetadefNamespace ORM class
should also indicate that the namespace column does not accept nulls
with "nullable=False" in the column definition.

Change-Id: I681747b6579a2284f23bf154889a61c639b0616d
Closes-Bug: 1367619

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