Use check.C.MkDir() instead of manual ioutil.TempDir() calls

This saves us at least 2 lines (error check, and cleanup) on every
instance, or in some cases adds cleanup that we forgot.

This is inspired by, but not directly related to, Go 1.15's addition of
Testing.T.TempDir.

NOTE: This might significantly increase the tests' disk space requirements;
AFAICS the temporary directories are only cleaned up when a whole "suite
finishes running.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

integration/registry.go

@@ -20,7 +20,6 @@ const (
 type testRegistryV2 struct {
 	cmd      *exec.Cmd
 	url      string
-	dir      string
 	username string
 	password string
 	email    string
@@ -45,10 +44,7 @@ func setupRegistryV2At(c *check.C, url string, auth, schema1 bool) *testRegistry
 }
 
 func newTestRegistryV2At(c *check.C, url string, auth, schema1 bool) (*testRegistryV2, error) {
-	tmp, err := ioutil.TempDir("", "registry-test-")
-	if err != nil {
-		return nil, err
-	}
+	tmp := c.MkDir()
 	template := `version: 0.1
 loglevel: debug
 storage:
@@ -86,7 +82,6 @@ http:
 		return nil, err
 	}
 	if _, err := fmt.Fprintf(config, template, tmp, url, htpasswd); err != nil {
-		os.RemoveAll(tmp)
 		return nil, err
 	}
 
@@ -98,7 +93,6 @@ http:
 	cmd := exec.Command(binary, confPath)
 	consumeAndLogOutputs(c, fmt.Sprintf("registry-%s", url), cmd)
 	if err := cmd.Start(); err != nil {
-		os.RemoveAll(tmp)
 		if os.IsNotExist(err) {
 			c.Skip(err.Error())
 		}
@@ -107,7 +101,6 @@ http:
 	return &testRegistryV2{
 		cmd:      cmd,
 		url:      url,
-		dir:      tmp,
 		username: username,
 		password: password,
 		email:    email,
@@ -130,6 +123,4 @@ func (t *testRegistryV2) tearDown(c *check.C) {
 	// It’s undocumented what Kill() returns if the process has terminated,
 	// so we couldn’t check just for that. This is running in a container anyway…
 	_ = t.cmd.Process.Kill()
-	err := os.RemoveAll(t.dir)
-	c.Assert(err, check.IsNil)
 }