tests/test-vm.sh: reduce default connection retries to 60 + use globa…

…l timeout of 5 minutes

There's no point in waiting ~45 minutes before timing out on our GitHub
action runs. Instead reduce retries from 180 to 60, and set overall
runtime of 5 minutes, which should be enough for our current builds.

tests/test-vm.sh

@@ -115,7 +115,8 @@ if [ "$success" = "0" ] ; then
 fi
 
 "$TEST_PWD"/tests/serial-console-connection \
-  --tries 180 \
+  --timeout 300 \
+  --tries 60 \
   --port "$serial_port" \
   --hostname "$VM_HOSTNAME" \
   --poweroff \