test: test buildroot read_with_timeout function

- Added a new stage that is stuck in an infinite loop
- Added two tests that use this stage and force a timeout

stages/org.osbuild.test.timeout

@@ -0,0 +1,20 @@
+#!/usr/bin/python3
+"""
+Test stage that is used for timeout tests
+"""
+
+import time
+import sys
+
+def main():
+
+    print('Test stage output.')
+    while True:
+        time.sleep(2)
+
+    return 0
+
+
+if __name__ == '__main__':
+    r = main()
+    sys.exit(r)