fork process may finish before cancel callback

* The "should we cancel?" callback check is only called while the
subprocess (child) is alive. If the child executes quickly, the cancel
callback has no chance to run.
* call a subprocess that takes longer to run like sleep 2

awx/main/tests/unit/expect/test_expect.py

@@ -90,7 +90,7 @@ def test_cancel_callback_error():
 
     extra_fields = {}
     status, rc = run.run_pexpect(
-        ['ls', '-la'],
+        ['sleep', '2'],
         HERE,
         {},
         stdout,