lnrpc: add "waiting to start" state to state service

This commit adds a new "waiting to start" state which may be used to
query if we're still waiting to become the cluster leader. Once leader
we advance the state to "wallet not exist" or "wallet locked" given
wallet availablity.

walletunlocker/service.go

@@ -165,6 +165,12 @@ func New(chainDir string, params *chaincfg.Params, noFreelistSync bool,
 	}
 }
 
+// SetLoaderOpts can be used to inject wallet loader options after the unlocker
+// service has been hooked to the main RPC server.
+func (u *UnlockerService) SetLoaderOpts(loaderOpts []btcwallet.LoaderOption) {
+	u.loaderOpts = loaderOpts
+}
+
 func (u *UnlockerService) newLoader(recoveryWindow uint32) (*wallet.Loader,
 	error) {