Gets a list of all box objects in a pipeline. Performs a single GET.
		Args:
			pipeline_key	key for pipeline
			sort_by			in desc order by 'creationTimestamp' or 'lastUpdatedTimestamp'
							Not sure if it is supported
			returns 		(status code for the GET request, dict of boxes)

def get_pipeline_boxes(self, pipeline_key, sort_by = None):
		'''Gets a list of all box objects in a pipeline. Performs a single GET.
		Args:
			pipeline_key	key for pipeline
			sort_by			in desc order by 'creationTimestamp' or 'lastUpdatedTimestamp'
							Not sure if it is supported
			returns 		(status code for the GET request, dict of boxes) 
		'''
		if not pipeline_key:
			return requests.codes.bad_request, None

		uri = '/'.join([
						self.api_uri,
						self.pipelines_suffix,
						pipeline_key
						])
		
		if sort_by:
				if sort_by in ['creationTimestamp', 'lastUpdatedTimestamp']:
					uri += self.sort_by_postfix + sort_by
				else:		
					return requests.codes.bad_request, {'success' : 'False', 
												'error': 'sortBy needs to be \'creationTimestamp\', or \'lastUpdatedTimestamp\''}
		
		return self._req('get', uri)