Fix query mysql module

The query() function in modules/mysql.py was throwing the following error:

    ...
    File "/usr/lib/pymodules/python2.7/salt/modules/mysql.py", line 194, in query
        dbc = _connect(**(connection_args.update({'connection_db': database, 'connection_conv': conv})))
    TypeError: _connect() argument after ** must be a mapping, not NoneType

Moved connection_args.update() to a separate line since it returns None.

Also fixed backwards logic for checking dbc