Add clean.sh

clean.sh gets rid of all residue of running DevStack except installed
packages and pip modules.

And it eradicates rabbitmq-server and ts erlang dependencies as well as
the other RPC backends and databases.

Change-Id: I2b9a251a0a151c012bae85a5a2f9c2f72e7700be

lib/databases/mysql

@@ -10,6 +10,24 @@ set +o xtrace
 
 register_database mysql
 
+# Get rid of everything enough to cleanly change database backends
+function cleanup_database_mysql {
+    if is_ubuntu; then
+        # Get ruthless with mysql
+        stop_service $MYSQL
+        sudo aptitude purge -y ~nmysql-server
+        sudo rm -rf /var/lib/mysql
+        return
+    elif is_fedora; then
+        MYSQL=mysqld
+    elif is_suse; then
+        MYSQL=mysql
+    else
+        return
+    fi
+    stop_service $MYSQL
+}
+
 function recreate_database_mysql {
     local db=$1
     local charset=$2

lib/databases/postgresql

@@ -10,6 +10,20 @@ set +o xtrace
 
 register_database postgresql
 
+# Get rid of everything enough to cleanly change database backends
+function cleanup_database_postgresql {
+    stop_service postgresql
+    if is_ubuntu; then
+        # Get ruthless with mysql
+        sudo aptitude purge -y  ~npostgresql
+        return
+    elif is_fedora; then
+        uninstall_package postgresql-server
+    else
+        return
+    fi
+}
+
 function recreate_database_postgresql {
     local db=$1
     local charset=$2