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/openshift.go

@@ -33,10 +33,7 @@ type openshiftCluster struct {
 // in isolated test environment.
 func startOpenshiftCluster(c *check.C) *openshiftCluster {
 	cluster := &openshiftCluster{}
-
-	dir, err := ioutil.TempDir("", "openshift-cluster")
-	c.Assert(err, check.IsNil)
-	cluster.workingDir = dir
+	cluster.workingDir = c.MkDir()
 
 	cluster.startMaster(c)
 	cluster.prepareRegistryConfig(c)
@@ -262,10 +259,6 @@ func (cluster *openshiftCluster) tearDown(c *check.C) {
 		// so we couldn’t check just for that. This is running in a container anyway…
 		_ = cluster.processes[i].Process.Kill()
 	}
-	if cluster.workingDir != "" {
-		err := os.RemoveAll(cluster.workingDir)
-		c.Assert(err, check.IsNil)
-	}
 	if cluster.dockerDir != "" {
 		err := os.RemoveAll(cluster.dockerDir)
 		c.Assert(err, check.IsNil)