CASSANDRA-12311 changed the format of WRITE_FAILURE and READ_FAILURE responses in protocol dse_v1:
<numfailures> in Read_failure and Write_failure error message bodies (Section 9)
has been replaced with <reasonmap>. The <reasonmap> maps node IP addresses to
a failure reason code which indicates why the request failed on that node.
The existing code expects the v4 format and breaks.