Set stdin to nil for HyperV execs

We're seeing a bug where failed Podman commands can hang in the
test suite, but somehow un-hang on STDIN activity (e.g. pressing
enter). On Brent's vague suspicion that it was related to STDIN,
I disabled STDIN on all execs from HyperV, and the hangs
disappear. I don't know why this is, or why the hangs happen in
the first place, but since this seems to work and should not have
any negative consequences that I can think of, here we go.

[NO NEW TESTS NEEDED] I have no idea how to test this one.

Signed-off-by: Matt Heon <mheon@redhat.com>

pkg/machine/e2e/config_test.go

@@ -164,6 +164,7 @@ func runWrapper(podmanBinary string, cmdArgs []string, timeout time.Duration, wa
  }
  GinkgoWriter.Println(podmanBinary + " " + strings.Join(cmdArgs, " "))
  c := exec.Command(podmanBinary, cmdArgs...)
+ c.Stdin = nil
  session, err := Start(c, GinkgoWriter, GinkgoWriter)
  if err != nil {
  Fail(fmt.Sprintf("Unable to start session: %q", err))

pkg/machine/hyperv/machine.go

@@ -775,6 +775,8 @@ func (m *HyperVMachine) startHostNetworking() (string, machine.APIForwardingStat
 
  logrus.Debugf("Starting gvproxy with command: %s %v", gvproxyBinary, c.Args)
 
+ c.Stdin = nil
+
  if err := c.Start(); err != nil {
  return "", 0, fmt.Errorf("unable to execute: %s: %w", cmd.ToCmdline(), err)
  }
@@ -811,6 +813,8 @@ func (m *HyperVMachine) startHostNetworking() (string, machine.APIForwardingStat
  }
  }
 
+ fsCmd.Stdin = nil
+
  if err := fsCmd.Start(); err != nil {
  return "", 0, fmt.Errorf("unable to execute: %s %v: %w", executable, args, err)
  }