Always check for root disks unless MINIO_CI_CD is set (#14232)

The current code considers a pool with all root disks to be as part
of a testing environment even if there are other pools with mounted
disks. This will result to illegitimate writing in root disks.

Fix this by simplifing the logic: require MINIO_CI_CD in order to skip
root disk check.

cmd/test-utils_test.go

@@ -111,7 +111,7 @@ func TestMain(m *testing.M) {
 
 	resetTestGlobals()
 
-	os.Setenv("MINIO_CI_CD", "ci")
+	globalIsCICD = true
 
 	os.Exit(m.Run())
 }