Detect replicating masters and fatal (also, warn on nonreplicating replicas)

Summary:
Ref T10759. Check master/replica status during startup.

After D16903, this also means that we check this status after a database comes back online after being unreachable.

If a master is replicating, fatal (since this can do a million kinds of bad things).

If a replica is not replicating, warn (this just means the replica is behind so some data is at risk).

Also: if your masters were actually configured properly (mine weren't until this change detected it), we would throw away patches as we applied them, so they would only apply to the first master. Instead, properly apply all migration patches to all masters.

Test Plan:

• Started Phabricator with a replicating master, got a fatal.
• Stopped replication on a replica, got a warning.
• With two non-replicating masters, upgraded storage.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10759

Differential Revision: https://secure.phabricator.com/D16904