Update the data migration current release to 'yoga'. 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.
Also add a reminder about this to the release cycle tasks list.
Change-Id: Ibdbeb752d29afeb48628587442577ab139be9ac9
Sem-Ver: api-break