Improve check of whether mysql is(/should be) running in default prepare script
We think the intention of the old version of this block is "if mysql is running, dump the databases". The check has been buggy for a long long time: it reads the contents of my.cnf ... which nowadays just has some !includedir directives. This lead to setting SOCKET="" and, it turns out, [ -S "" ] returns true. The main intention of this part of the prepare script is to backup vaguely normal machines running a simple mysql database, such as small group webservers. We thus don't need to consider every eventuality.