Update migration constant
Update migration constant

Update the data migration current release to 'zed'.  Include a
semver pseudo-header in this commit message so that pbr will
increment the major version number, otherwise
glance.tests.unit.gate.test_data_migration_version will break.

Change-Id: Iad32226cea6f81cb0a18a46f4f89ebd3dc42d9a9
Sem-Ver: api-break

openstack/glance,openstack/glance,openstack/glance