Votequorum: Fix auto_tie_breaker default

The default for auto_tie_breaker should be 'lowest' - which is what it
was before the extended ATB functionality of auto_tie_breaker_node was
added, and what the documentation states.

However this was broken so that if auto_tie_breaker_node was not
specified then auto_tie_breaker itself was ignored. This patch fixes
that.

It also fixes a typo in a comment.

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