Critical error during site deletion when using external MySQL host

During site deletion, the hostname for the site's MySQL user 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 GRANT host established in easyengine.conf, as the MySQL database host was stored in wp-config.php which would not be the same as the granted host/IP (as the granted IP would traditionally be the webserver). This critical error would leave the system in an incongruent state, as the database would have been dropped, but the MySQL user+ Nginx configuration + web root would not be touched.

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.