R1:ea182b6df9ec

When we failover to a replica, log the exception we hit

Summary: See PHI1180. Currently, when we failover to a replica, we may not log the failure. Failovers are serious business and bad news, so emit a log even if we are able to connect to the replica.

Test Plan:
Configured a bogus master and a good replica:

```
$ ./bin/mail list-outbound
[2019-03-29 16:26:09] PHLOG: 'Retrying (attempt 1) after connection failure ("AphrontConnectionQueryException", #2002): Attempt to connect to root@127.0.0.2 failed…