Fixed site deletion when using external MySQL host

During site deletion, the hostname for "GRANT" was pulled from the site specific wp-config.php file rather than  easyengine.conf. 

This caused a critical error to occur when using a external mysql host, as the MySQL database host was stored in wp-config.php which would not be the same as the granted host/IP (as that would traditionally be the webserver).

This simply checks if ee_lib_variables.sh changed the constant $EE_MYSQL_GRANT_HOST, and if it has been changed, modifies the ee_db_host variable to match.