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 with error #2002: Operation timed out.' at [/Users/epriestley/dev/core/lib/libphutil/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:124]
[2019-03-29 16:26:19] PHLOG: 'Retrying (attempt 2) after connection failure ("AphrontConnectionQueryException", #2002): Attempt to connect to root@127.0.0.2 failed with error #2002: Operation timed out.' at [/Users/epriestley/dev/core/lib/libphutil/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:124]
[2019-03-29 16:26:29] EXCEPTION: (PhutilProxyException) Failed to connect to master database ("local_config"), failing over into read-only mode. {>} (AphrontConnectionQueryException) Attempt to connect to root@127.0.0.2 failed with error #2002: Operation timed out. at [<phutil>/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:362]
<...snip backtrace...>
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...
```
Configured a bogus master and a bogus replica:
```
$ ./bin/mail list-outbound
[2019-03-29 16:26:57] PHLOG: 'Retrying (attempt 1) after connection failure ("AphrontConnectionQueryException", #2002): Attempt to connect to root@127.0.0.2 failed with error #2002: Operation timed out.' at [/Users/epriestley/dev/core/lib/libphutil/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:124]
[2019-03-29 16:27:07] PHLOG: 'Retrying (attempt 2) after connection failure ("AphrontConnectionQueryException", #2002): Attempt to connect to root@127.0.0.2 failed with error #2002: Operation timed out.' at [/Users/epriestley/dev/core/lib/libphutil/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:124]
[2019-03-29 16:27:27] PHLOG: 'Retrying (attempt 1) after connection failure ("AphrontConnectionQueryException", #2002): Attempt to connect to root@127.0.0.3 failed with error #2002: Operation timed out.' at [/Users/epriestley/dev/core/lib/libphutil/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:124]
[2019-03-29 16:27:37] PHLOG: 'Retrying (attempt 2) after connection failure ("AphrontConnectionQueryException", #2002): Attempt to connect to root@127.0.0.3 failed with error #2002: Operation timed out.' at [/Users/epriestley/dev/core/lib/libphutil/src/aphront/storage/connection/mysql/AphrontBaseMySQLDatabaseConnection.php:124]
[2019-03-29 16:27:47] EXCEPTION: (PhabricatorClusterStrandedException) Unable to establish a connection to any database host (while trying "local_config"). All masters and replicas are completely unreachable.
AphrontConnectionQueryException: Attempt to connect to root@127.0.0.2 failed with error #2002: Operation timed out. at [<phabricator>/src/infrastructure/storage/lisk/PhabricatorLiskDAO.php:177]
<...snip backtrace...>
```
Reviewers: amckinley
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20351