Use unique passwords for replication user

Generates a unique user with a random password for each slave.
The replication user and password is passed to each slave during
the snapshot attach process.  Replication user is deleted from
both the master and the slave during the detach process.

Co-Authored-By: Nikhil Manchanda <SlickNik@gmail.com>
Co-Authored-By: Denis Makogon <dmakogon@mirantis.com>

Change-Id: I9cb158a161714bfff90225227f5c652120393ba7
Closes-bug: 1357065
Merge "Use unique passwords for replication user"