mysql_lvm mysqldump missing check after wait_for_mysqld

[MikeG]

If mysqld exits very quickly (such as when unix permissions prevent creation of a pid), the following code returns to MySQLDumpDispatchAction and a mysqldump is attempted:

https://github.com/holland-backup/holland/blob/v1.0.10/plugins/holland.backup.mysql_lvm/holland/backup/mysql_lvm/actions/mysql/mysqldump.py#L55

Since mysqld exited already, mysqldump fails with mysqldump: Got error: 2002: Can't connect to local MySQL server through socket (2)

Then the snapshot is unmounted and you see a seemingly deferred error:

 [ERROR] [Errno 3] No such process

Related: https://bugs.launchpad.net/holland-backup/+bug/1194979