Tiller should only enforce what we expect from Helm

https://github.com/kubernetes/helm/pull/3183 added a keepalive to the Helm client of 30s period, while Tiller was never configured to permit this, keeping the default minimum keepalive period of 5 minutes, disconnecting any clients which ping more regularly than this.

This commit enforces a minimum that is lower than what Helm is configured for, preventing these disconnections, and thus fixes #3409.

(cherry picked from commit 588f7a84)

cmd/tiller/tiller.go

@@ -161,6 +161,9 @@ func start() {
 			MaxConnectionIdle: 10 * time.Minute,
 			// If needed, we can configure the max connection age
 		}))
+		opts = append(opts, grpc.KeepaliveEnforcementPolicy(keepalive.EnforcementPolicy{
+			MinTime: time.Duration(20) * time.Second, // For compatibility with the client keepalive.ClientParameters
+		}))
 	}
 
 	rootServer = tiller.NewServer(opts...)