MariaDB support

I'm running MariaDB locally (as probably many people) and the tests are not passing for me. They fail on `unknown variable 'set-gtid-purged=off'` This option was added in #348 as a param to `mysqldump`. But it seems to be Oracle MySQL only and not supported by MariaDB. Which also means that schema dumping and loading probably does not work against MariaDB.

Another issue is that I'm getting a lot of warning like this (because we hardcode `mysql` binary name):

```
mysql: Deprecated program name. It will be removed in a future release, use '/usr/bin/mariadb' instead
```

Which also means that MariaDB will simply not work in the future, when they release a new version.

So I think the first question is: should we support it? If not, probably worth a note somewhere. If yes, I can propose some plan to add support for both flavours.

The issue names no files or test paths; start by reproducing the failing tests with MariaDB and tracing the mysqldump option introduced in #348. Inspect the hardcoded mysql binary and the schema dumping and loading paths. Done requires an explicit support decision, with working tests and compatible binary handling if support is chosen, or a clear documentation note otherwise.

Written by the indexing model from the issue text.