feat: Disable concurrency if any release is using tillerless (#694)

So that you don't need to remember adding `--concurrency 1`

README.md

@@ -707,9 +707,6 @@ With the [helm-tiller](https://github.com/rimusz/helm-tiller) plugin installed,
 To enable this mode, you need to define `tillerless: true` and set the `tillerNamespace` in the `helmDefaults` section
 or in the `releases` entries.
 
-Since every commands is run with `helm tiller run ...`, you have to disable concurrency. Otherwise you'll get
-mysterious errors about the tiller daemon.
-
 ## Separating helmfile.yaml into multiple independent files
 
 Once your `helmfile.yaml` got to contain too many releases,

pkg/state/state_run.go

@@ -19,6 +19,16 @@ func (st *HelmState) scatterGather(concurrency int, items int, produceInputs fun
 		concurrency = numReleases
 	}
 
+	for _, r := range st.Releases {
+		if r.Tillerless != nil {
+			if *r.Tillerless {
+				concurrency = 1
+			}
+		} else if st.HelmDefaults.Tillerless {
+			concurrency = 1
+		}
+	}
+
 	// WaitGroup is required to wait until goroutine per job in job queue cleanly stops.
 	var waitGroup sync.WaitGroup
 	waitGroup.Add(concurrency)