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.

lnwallet/btcwallet/btcwallet_integration.go

@@ -0,0 +1,23 @@
+//go:build integration || lowscrypt
+
+package btcwallet
+
+import (
+	"github.com/btcsuite/btcwallet/snacl"
+	"github.com/btcsuite/btcwallet/waddrmgr"
+)
+
+func init() {
+	// Instruct waddrmgr to use the cranked down scrypt parameters when
+	// creating new wallet encryption keys. This will speed up the itests
+	// considerably.
+	fastScrypt := waddrmgr.FastScryptOptions
+	keyGen := func(passphrase *[]byte, config *waddrmgr.ScryptOptions) (
+		*snacl.SecretKey, error) {
+
+		return snacl.NewSecretKey(
+			passphrase, fastScrypt.N, fastScrypt.R, fastScrypt.P,
+		)
+	}
+	waddrmgr.SetSecretKeyGen(keyGen)
+}