Changed defaults-file to defaults-extra-file

Should load the .my.cnf file with "--defaults-extra-file" instead of "--defaults-file". This is necessary if we have global my.cnf file but we want to use both of them.
Fixed missing parent for global mysql class

Added "require" to the global mysql.rb file like in the other provider files.

defaults-file changed to defaults-extra-file in all the database_* (old) providers, the same as in the mysql_* providers.

Changed defaults-file to defaults-extra-file in all test files
Merge pull request #367 from w32-blaster/master

Method for loading .my.cnf file is changed from "defaults-file" to "defaults-extra-file" (mysql option)