Implement addAdbPublicKey endpoint

Reason: manually approve adb connection from web UI does not scale for test automation. Especially those that are using different adb keys on each session (eg: via container)

This changes also added swagger doc endpoint. Using `stf local` command, it will end up at: `http://localhost:7106/docs/`

lib/units/api/index.js

@@ -4,6 +4,7 @@ var events = require('events')
 
 var express = require('express')
 var SwaggerExpress = require('swagger-express-mw')
+var SwaggerUi = require('swagger-tools/middleware/swagger-ui');
 var cookieSession = require('cookie-session')
 var Promise = require('bluebird')
 var _ = require('lodash')
@@ -71,6 +72,7 @@ module.exports = function(options) {
     if (err) {
       throw err
     }
+    app.use(SwaggerUi(swaggerExpress.runner.swagger));
     swaggerExpress.register(app)
   })