OPENDJ-3041 Strictly select the backend where an entry reside taking into account all child backends

A side effect of fixing OPENDJ-2946 is the selection of which backend should contain a given entry.
We were basing the choice on the longest match for the backend, but if there are backends who are
sub-suffixes of another, it does not work.
Revert to scan the list of backends for a match or walking the parent DNs of the entry, depending of which we deem the fastest