Don't run any excess mysqld processes in bootstrap mode, but let mysql_upgrade
take care of all database conversions and upgrade tricks. We can never have
all of mysql_upgrade contents as part of the mariadb-server postinstall script,
so don't even attempt it. A better approach is to patch mysql_upgrade is something
extra is needed.

Merge suitable parts of upstream commit
https://github.com/MariaDB/server/commit/7f6d88944c8afdcba12677840db8bc4e81cbe0db

Also drop legacy user table Password column fix dropped in upstream commit
https://github.com/MariaDB/server/commit/60ad33984090af2262d17232ceab1c1c9231fd24

Re-implement plugin rename similar to as done in upstream commit
https://github.com/mariadb/server/commit/fdfdea40f1b9d029de59131f54096c1b044ffdfa