R1:5a0b7398cabd

Give bin/storage some replica-aware options

Summary:
Fixes T10758.

- Adds a "--host" flag. If you specify this, we read your cluster config. This lets you dump from a replica.
- Adds a "--for-replica" flag to `storage dump`. This makes `mysqldump` include a `CHANGE MASTER ...` statement in the output, which is useful when setting up a replica for the first time.

Test Plan:
- Dumped master and replica cluster databases.
- Dumped non-cluster databases.
- Ran various other commands (help, status…