Various fixes to the mysql module to break out the handling of user m…

…anagement into different functions based on MySQL variant.

Minor tweak to mysql module.  Fixing failing tests.

Reworking the unix_socket code to support the differences between MySQL and MariaDB.  Adding some functions to install, remove, and check the status of plugins which we can then use when adding users which will use the unix_socket & auth_socket plugins. Adding additional tests for these new functions as well as test to ensure the correct SQL is being generated when using passwordless and unix_socket options.

Ensure _mysql_user_exists is using auth_socket.  Updating mysql and mariadb chpass functions to ensure that the respective plugins are enabled before attempting to use them.

Adding better error reporting around plugins.  Updating tests.  Only attempt to delete a user if they exist.

Removing quotes from the plugin_status query.  Updating tests to reflect changes.