votequorum: Change check of expected_votes

Previously value of new expected_votes was checked so newly computed
quorum value was in the interval <total_votes / 2, total_votes>. The
upper range prevented the cluster to become unquorate, but bottom check
was almost useless because it allowed to change expected_votes so it is
smaller than total_votes.

Solution is to check if expected_votes is bigger or equal to total_votes
and for quorate cluster only check if cluster doesn't become unquorate
(for unquorate cluster one can set upper range freely - as it is
perfectly possible when using config file)

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