Add latest commit info reachable through API

After call to /api/peers/version return build info if lisk was installed from binaries or last commit if installed using source.

closes LiskArchive#340

helpers/git.js

@@ -0,0 +1,13 @@
+'use strict';
+var childProcess = require('child_process');
+
+/**
+ @throws Will throw an error if the git is not installed or not a git repository.
+ */
+function getLastCommit() {
+    return childProcess.execSync('git rev-parse HEAD').toString().trim();
+}
+
+module.exports = {
+    getLastCommit: getLastCommit
+};

modules/peers.js

@@ -6,6 +6,7 @@ var constants = require('../helpers/constants.js');
 var extend = require('extend');
 var fs = require('fs');
 var ip = require('ip');
+var git = require('../helpers/git.js');
 var OrderBy = require('../helpers/orderBy.js');
 var path = require('path');
 var Peer = require('../logic/peer.js');
@@ -544,7 +545,14 @@ shared.getPeer = function (req, cb) {
 };
 
 shared.version = function (req, cb) {
-	return setImmediate(cb, null, {version: library.config.version, build: library.build});
+	try {
+    	var response = library.build ? {build: library} : {commit: git.getLastCommit()};
+        response.version = library.config.version;
+        return setImmediate(cb, null, response);
+	}
+	catch (err) {
+    	return setImmediate(cb, 'Git is not installed or not a git repository');
+	}
 };
 
 // Export

test/api/peers.js

@@ -4,10 +4,10 @@ var node = require('./../node.js');
 
 describe('GET /api/peers/version', function () {
 
-	it('should be ok', function (done) {
+	it('should be working with sources', function (done) {
 		node.get('/api/peers/version', function (err, res) {
 			node.expect(res.body).to.have.property('success').to.be.ok;
-			node.expect(res.body).to.have.property('build').to.be.a('string');
+			node.expect(res.body).to.have.property('commit').to.be.a('string');
 			node.expect(res.body).to.have.property('version').to.be.a('string');
 			done();
 		});