I103: Duplicated topics are returned

Duplicated topics were being returned when a second query was run but the
index did not properly slice the results due to looking for the offset-key
options instead of offset-id.  I don't think it was ever intended for this
to be two options so all offset-key usages were replaced with offset-id
and a test was written to verify it slices in the appropriate place.

Change-Id: I2f8d69730b8a88e6270b7408922d4775accf7039