Attempt to get device type from the image first partition

New images will ship a `device-type.json` file in the first partition,
which we can use instead of querying the API for certain configuration
and initialisation commands.

If the file is not found, or is malformed, we still fallback to the API.

Signed-off-by: Juan Cruz Viotti <jviotti@openmailbox.org>

lib/utils/helpers.coffee

@@ -19,6 +19,9 @@ capitano = Promise.promisifyAll(require('capitano'))
 _ = require('lodash')
 _.str = require('underscore.string')
 president = Promise.promisifyAll(require('president'))
+resin = require('resin-sdk')
+imagefs = require('resin-image-fs')
+rindle = require('rindle')
 os = require('os')
 chalk = require('chalk')
 
@@ -52,3 +55,18 @@ exports.sudo = (command, message) ->
 		console.log('Type your computer password to continue')
 
 	return president.executeAsync(command)
+
+exports.getManifest = (image, deviceType) ->
+
+	# Attempt to read manifest from the first
+	# partition, but fallback to the API if
+	# we encounter any errors along the way.
+	imagefs.read
+		image: image
+		partition:
+			primary: 1
+		path: '/device-type.json'
+	.then(rindle.extractAsync)
+	.then(JSON.parse)
+	.catch ->
+		resin.models.device.getManifestBySlug(deviceType)