Clean /etc/mysql when calling clean.sh

The clean.sh script should also remove the /etc/mysql
directory. It contains information from the old
devstack installation and may conflict with the further
one. apt-get purge does not remove it since the
directory is not empty.

Change-Id: I885345a2311851d8746abe42e44300ecd4f6e08a

lib/databases/mysql

@@ -23,6 +23,7 @@ function cleanup_database_mysql {
         stop_service $MYSQL
         apt_get purge -y mysql*
         sudo rm -rf /var/lib/mysql
+        sudo rm -rf /etc/mysql
         return
     elif is_fedora; then
         if [[ $DISTRO =~ (rhel7) ]]; then