Make sure we are trying to unmount a mounted /etc/resolv.conf

Signed-off-by: Alvaro Saurin <alvaro.saurin@gmail.com>

integration-cli/docker_cli_run_test.go

@@ -1448,10 +1448,16 @@ func (s *DockerSuite) TestRunResolvconfUpdate(c *check.C) {
 	// This test case is meant to test monitoring resolv.conf when it is
 	// a regular file not a bind mounc. So we unmount resolv.conf and replace
 	// it with a file containing the original settings.
-	cmd := exec.Command("umount", "/etc/resolv.conf")
-	if _, err = runCommand(cmd); err != nil {
+	mounted, err := mount.Mounted("/etc/resolv.conf")
+	if err != nil {
 		c.Fatal(err)
 	}
+	if mounted {
+		cmd := exec.Command("umount", "/etc/resolv.conf")
+		if _, err = runCommand(cmd); err != nil {
+			c.Fatal(err)
+		}
+	}
 
 	//cleanup
 	defer func() {