Update marconi.conf-sample to deprecate sqlite

Now we're supporting sqlalchemy and the sqlite is deprecated.
So the marconi.conf-sample should be update to reflect the
change so as to avoid confusion.

Closes-Bug: #1288619

Change-Id: Ief5dad6345dc24e70af18e9e47d0f8dd384cee47
Merge "Update marconi.conf-sample to deprecate sqlite"