tests: Add espflash flash --monitor tests

espflash/tests/scripts/flash.sh

@@ -1,7 +1,12 @@
 #!/usr/bin/env bash
 
-result=$(espflash flash --no-skip $1 2>&1)
+result=$(timeout 8s espflash flash --no-skip --monitor --non-interactive $1 2>&1)
 echo "$result"
 if [[ ! $result =~ "Flashing has completed!" ]]; then
+    echo "Flashing failed!"
+    exit 1
+fi
+if ! echo "$result" | grep -q "Hello world!"; then
+    echo "Monitoring failed!"
     exit 1
 fi