Add option to use mydumper for backups

[lizrea]

MyDumper does tablewise backups in a threaded manner, it's a better solution for MariaDB backups. Let's have an alternate tool available to do that.

[tomascohen]

Is the backup feature something we want to maintain inside Aspen? Or vendor/deployment dependent? I'm open to any option, just wondering.

[mdnoble73]

It's been nice having backup options available within the Aspen codebase to make backups easier. That also allows them to be monitored by the monitoring API to ensure backups are being done and give warnings or errors if they are not.

[tomascohen]

In that case, I support the idea from @lizrea about using mydumper which is awesome.