votequorum: Reflect runtime change of 2Node to WFA

When 2Node mode is set, WFA is also set unless WFA is configured
explicitly. This behavior was not reflected on runtime change, so
restarted corosync behavior was different (WFA not set). Also when
cluster is reduced from 3 nodes to 2 nodes during runtime, WFA was not
set, what may result in two quorate partitions.

Solution is to set WFA depending on 2Node when WFA
is not explicitly configured.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>