metrics: fixes common.sh function to always return true

This PR corrects the init env() helper function, to make that
systemctl always returns true when enumerating masked services,
and preventing the test from failing

Fixes: kata-containers#8242

Signed-off-by: David Esparza <david.esparza.borquez@intel.com>

tests/metrics/lib/common.bash

@@ -175,7 +175,7 @@ function init_env()
 	clean_env_ctr
 
 	# restart docker only if it is not masked by systemd
-	docker_masked="$(systemctl list-unit-files --state=masked | grep -c docker)"
+	docker_masked="$(systemctl list-unit-files --state=masked | grep -c docker)" || true
 	if [ "${docker_masked}" -eq 0 ]; then
 		sudo systemctl restart docker
 	fi
@@ -191,7 +191,7 @@ function init_env()
 # killed to start test with clean environment.
 function kill_processes_before_start()
 {
-	docker_masked="$(systemctl list-unit-files --state=masked | grep -c "${DOCKER_EXE}")"
+	docker_masked="$(systemctl list-unit-files --state=masked | grep -c "${DOCKER_EXE}")" || true
 
 	if [ "${docker_masked}" -eq 0 ]; then
 		DOCKER_PROCS=$(sudo "${DOCKER_EXE}" ps -q)