[SO] Use common secret template in so

[SO] Use common secret template in so

Generate passwords for:
- so_user
- so_admin

and distribute them to all SO subcharts.

mariadb-galera root password is taken as a reference to existing
secret (shared mariadb instance) or also generated if local cluster is
used.

Three other DB users also have generated passwords but they are not
distributed outside of so-mariadb as they were never used.

Issue-ID: OOM-2328
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Change-Id: Ic4af5c9b12b00d2a52d2597e3fe1161d0d1a9f20