CMSettings: don't trample user metrics setting on upgrade

During an upgrade, we try to migrate values which are
considered to be LEGACY settings to the new provider, however
because of a bad upgrade path, we need to check if the key exists in the
new database AND the old database, and then we can skip it in that case.

Ticket: CYNGNOS-2740

Change-Id: I5d6bc8399ccc328f4190ed7508c27bd9d5de1b9d
Signed-off-by: Roman Birg <roman@cyngn.com>
(cherry picked from commit 256a7350)