Make ERP5 SR able to deploy an ERP5 cluster.
Add a mysql_tzinfo_to_sql wrapper for mariadb and remove --no-default param

vincent: Minor fixes. Move branch switch to a separate commit.
Reduce the number of databases created by default.

Should still be sufficient for ERP5 unit tests: largest test uses 3 DB, and
we want to run 10 tests in parallel.
Switch branch.