* Fix UNION syntax in resourcepermissions package.
* Fix migrations in usermig package to work with Spanner.
* Fix health query.
* Use more connections for integration tests.
* Add test-go-integration-spanner target to run integration tests against Spanner emulator.
* Add test for enterprise.
* Don't delete sequence number for migration_log.id column.
* Only bump max open connections to 20 for Spanner.
Lower integration test timeout.