Add migration script for Ghost CLI -> Docker installs

- This script handles the copy of both assets and the MySQL database
  from an existing install to a new Docker based install
- Its currently been tested on the "happy path" of a Ghost CLI install
  and works

mysql-init/create-multiple-databases.sh

@@ -6,7 +6,7 @@ set -u
 if [ -n "$MYSQL_MULTIPLE_DATABASES" ]; then
   echo "Creating multiple databases: $MYSQL_MULTIPLE_DATABASES"
 
-  for db in $(echo $MYSQL_MULTIPLE_DATABASES | tr ',' ' '); do
+  for db in $(echo "$MYSQL_MULTIPLE_DATABASES" | tr ',' ' '); do
     echo "Creating database: $db"
     mysql -u root -p"$MYSQL_ROOT_PASSWORD" <<-EOSQL
       CREATE DATABASE IF NOT EXISTS \`$db\`;