qnet: Add support for keep active partition vote

qnet: Add support for keep active partition vote

This patch adds qdevice-net part of keep active partition tie breaker
functionality. It's enabled by default.

When tie happens prefer partition with members of
previously active (quorate) partition. This is hard-coded
behavior of LMS algorithm so this setting affects only
FFSplit algorithm. By default it is disabled for backwards
compatibility.

This solves problem with FFSplit when node A (with lowest id) is killed,
node B gets vote and then node A starts up and creates single node
membership and gets vote.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>