COOK-4547: Shellescape server_root_password

With this change, we can finally use spaces, exclamation marks, and "\`rm -rf /\`" as root_password.

[I did some smoke testing](https://github.com/srenatus/mysql/commit/01a747325b6c92a267e2c3cfb2a13505b5181592) in TK, some more testing might still be advisable.