Tests using MW-369.inc sometimes hanged after
signaling two debug sync points inside a Galera
library. Replaced Galera library sync point
with server code sync point when possible and
added more wait_conditions to make sure we are
in correct state.

Tests effected: MW-369, MW-402, MDEV-27276, and
mysql-wsrep#332.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>