Fix non-Primary checks in liveness probe

The liveness probe did not parse non-Primary condition out
of the mysql CLI command. Consequently, the liveness did not fail
whe a galera node was disconnected from the primary partition and
the galera pod could not restart automatically, leading to long
delays before restart or sometimes full cluster disruption.

Fix the way probes are handled and refactors bits to allow more
precise conditions in startup/readiness/liveness probes.

Jira: OSPRH-8862

Author: dciabrin

templates/galera/bin/mysql_probe.sh

@@ -1,27 +1,37 @@
 #!/bin/bash
-set -eu
+set -u
 
 # This secret is mounted by k8s and always up to date
 read -s -u 3 3< /var/lib/secrets/dbpassword MYSQL_PWD || true
 export MYSQL_PWD
 
 PROBE_USER=root
+function mysql_status_check {
+    local status=$1
+    local expect=$2
+    set -x
+    mysql -u${PROBE_USER} -sNEe "show status like '${status}';" | tail -1 | grep -w -e "${expect}"
+}
 
 # Consider the pod has "started" once mysql is reachable
+# and is part of the primary partition
 if [ "$1" = "startup" ]; then
-    mysql -u${PROBE_USER} -sNe "select(1);"
+    mysql_status_check wsrep_cluster_status Primary
     exit $?
 fi
 
-set -x
+# readiness and liveness probes are run by k8s only after start probe succeeded
 
 case "$1" in
     readiness)
         # If the node is e.g. a donor, it cannot serve traffic
-        mysql -u${PROBE_USER} -sNe "show status like 'wsrep_local_state_comment';" | grep -w -e Synced;;
+        mysql_status_check wsrep_local_state_comment Synced
+        ;;
     liveness)
-        # If the node is not in the primary partition, restart it
-        mysql -u${PROBE_USER} -sNe "show status like 'wsrep_cluster_status';" | grep -w -e Primary;;
+        # If the node is not in the primary partition, the failed liveness probe
+        # will make k8s restart this pod
+        mysql_status_check wsrep_cluster_status Primary
+        ;;
     *)
         echo "Invalid probe option '$1'"
         exit 1;;