CPERF: Disable CSIT IPv6 suite

This suite is failing with disconnects for the SSH connection to the
overcloud controller. Disabling it for now until we can figure out what
the problem is. Only happens in this suite:
https://build.opnfv.org/ci/job/cperf-apex-csit-master/104/consoleFull

Change-Id: I15eda3009f181c190bcef6e51b00d22070d9e444
Signed-off-by: Tim Rozet <trozet@redhat.com>