Controller shutdown error: Unable to release shared lock to the database

[talanknight]

Describe the bug
When shutting down a controller an error is returned "Unable to release shared lock to the database: schema.(Manager).SharedUnlock: postgres.(Postgres).UnlockShared: unknown, unknown: error #0: driver: bad connection"

To Reproduce
Steps to reproduce the behavior, In boundary version 0.1.5:

1. Make sure that config.hcl has a controller section with a database url specified.
2. Run boundary database init -config config.hcl
3. Run boundary server -config config.hcl
4. Wait for controller to finish starting and hit ctrl-C
5. See error "Unable to release shared lock to the database: schema.(Manager).SharedUnlock: postgres.(Postgres).UnlockShared: unknown, unknown: error #0: driver: bad connection"

Expected behavior
No error returned

Additional context
The error indicates that the connection to the database was not in a state that allowed releasing the lock. Since this is a postgres advisory lock it should be getting released when the connection to the database is closed. If this happens while the controller is still running it could make it possible for database migrate to happen while the controller is still running.