fixed a problem with the mysql_database provider

There are two problems with the query generated in the ```instances``` method of the mysql_database provider.  They show themselves when we try to remove the default accounts:

1. The quoting is wrong.  We needed single quotes around the ```%_database``` part of the query.
2. I'm not sure what the ```name``` parameter inside the array passed to ```mysql``` command is intended to do, but it appears to be generating queries with the database name in it, such as  ```show variables like '%_database' information_schema```, which won't run.

This pull request fixes both of those issues.