small fixes to spec & http_server & Vagrantfile (#2859)

* Vagrantfile: install dev_tools

Follow-up on https://github.com/tendermint/tendermint/pull/2824

* update consensus params spec

* fix test name

* rpc_test: panic if failed to start listener

also
- remove http_server#MustListen
- align StartHTTPServer and StartHTTPAndTLSServer functions

* dep: allow minor releases for grpc

rpc/lib/rpc_test.go

@@ -134,6 +134,9 @@ func setup() {
 	wm.SetLogger(unixLogger)
 	mux2.HandleFunc(websocketEndpoint, wm.WebsocketHandler)
 	listener2, err := server.Listen(unixAddr, server.Config{})
+	if err != nil {
+		panic(err)
+	}
 	go server.StartHTTPServer(listener2, mux2, unixLogger)
 
 	// wait for servers to start