Update comments

- updates comments and adds where missing
- updates locks so that unlock is done via defer instead of
at the end of the statement
- extracts timeout variable in two places
- remove makeClient() unused method from metrics package

No-harm changes tested via go build.

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

gateway/requests/requests.go

@@ -1,6 +1,8 @@
 // Copyright (c) Alex Ellis 2017. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+// Package requests package provides a client SDK or library for
+// the OpenFaaS gateway REST API
 package requests
 
 // CreateFunctionRequest create a function in the swarm.