Prepare db migration.

Prepare db migration.

Note:
 * migration must not alter the old db, so we should create a new db and a
   user with only read privileges on previous db.
 * migration procedure will contain at least 4 steps:
   1 - copy old tables that will still exist in the new db
   2 - create new tables
   3 - perform data insertion
   4 - remove temporary tables

Signed-off-by: Florent Bruneau <florent.bruneau@polytechnique.org>