multi: add new build tag integration

This commit adds a new build tag `integration` and removes the old tag
`rpctest` for clarity. Multiple unnecessary usages of `build !rpctest`
is also removed.

funding/config_integration.go

@@ -0,0 +1,11 @@
+//go:build integration
+
+package funding
+
+import "time"
+
+func init() {
+	// For itest, we will use a much shorter checking interval here as
+	// local communications are very fast.
+	checkPeerFundingLockInterval = 10 * time.Millisecond
+}