test: use utils.check_output for daemonization

The open-coded subprocess.Popen sequence in Microvm.spawn was equivalent
to `utils.check_output(..., shell=False)`, so just use that.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

tests/framework/microvm.py

@@ -594,14 +594,7 @@ def spawn(
         # When the daemonize flag is on, we want to clone-exec into the
         # jailer rather than executing it via spawning a shell.
         if self.jailer.daemonize:
-            res = subprocess.Popen(
-                cmd,
-                stdout=subprocess.PIPE,
-                stderr=subprocess.PIPE,
-            )
-            stdout, stderr = res.communicate()
-            if res.returncode != 0:
-                raise RuntimeError(res.returncode, stdout, stderr)
+            utils.check_output(cmd, shell=False)
         else:
             # Run Firecracker under screen. This is used when we want to access
             # the serial console. The file will collect the output from

tests/integration_tests/security/test_jail.py

@@ -533,7 +533,7 @@ def test_negative_no_file_limit(uvm_plain):
     # pylint: disable=W0703
     try:
         test_microvm.spawn()
-    except RuntimeError as error:
+    except ChildProcessError as error:
         assert "No file descriptors available (os error 24)" in str(error)
     else:
         assert False, "Negative test failed"