Reviewer Mike - Use QUORUM reads if ONE reads don't return any values

As we've discussed, this causes homer/homestead to try to read with consistency ONE, but to try again with consistency QUORUM if the first read fails to find any records.  I've tested this against your broken homestead nodes and saw that we'd consistently get the records back (I added logging and checked that it was doing the two reads).

All UTs pass after making them expect us to call `safe_get` and `safe_get_slice` rather than `cass.get` and `cass.get_slice`.