Correcting the right path to mysql log in Fedora 19

The mysql log is wrong in Fedora 19+ pointing to
/var/lib/mysqld.log while the correct is /var/log/mysqld.log.
This make the job fail if you're running Fedora with
mysql.
This error was inserted by
https://review.openstack.org/#/c/55827/

Change-Id: I63dd494f1ae105ad007344dea40936ab283d55a9

devstack-vm-gate.sh

@@ -280,7 +280,7 @@ else
     # the path are different for fedora and red hat.
     if [ -f /usr/bin/yum ]; then
         POSTGRES_LOG_PATH="-d /var/lib/pgsql"
-        MYSQL_LOG_PATH="-f /var/lib/mysqld.log"
+        MYSQL_LOG_PATH="-f /var/log/mysqld.log"
     else
         POSTGRES_LOG_PATH="-d /var/log/postgresql"
         MYSQL_LOG_PATH="-d /var/log/mysql"