Fix mysql __virtual__ to correctly detect config
Fix mysql __virtual__ to correctly detect config

It looks like when the following commit[1] was made it broke the mysql
module, and I haven't noticed until now some how.

My guess is that __opts__ used to look like
__opts__['mysql']['default_file'] where as it now looks like
__opts__['mysql.default_file']

[1] = https://github.com/saltstack/salt/commit/b7e7cc3cb1ede997d4af3a3ea2826d6f80ab2dcf

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt