Issue 50937 - Update CLI for new backend split configuration
Description: In preparation for the move to LMDB the global database
configuration has been split into two (or more) entries
under cn=config. This patch changes how the gets/sets
work to make both of these entries appear as one
configuration unit. This is done by dynamically setting
the backend configuration entry dn with what is set in
nsslapd-backend-implement.
relates: https://pagure.io/389-ds-base/issue/50937
Reviewed by: spichugi, tbordaz, and firstyear(Thanks!!!)
Make changes via Simon's suggestions
Add firstyear's assert