Use vendored Python dependencies

.gitignore

@@ -1 +1,2 @@
 target
+*pyc

.taskcluster.yml

@@ -21,7 +21,7 @@ tasks:
 
       payload:
         maxRunTime: 600
-        image: "python:2.7.15-stretch"
+        image: "buildpack-deps:bionic-scm"
         features:
           taskclusterProxy: true
         env:
@@ -35,5 +35,4 @@ tasks:
             git clone ${event.repository.clone_url} repo &&
             cd repo &&
             git checkout ${event.after} &&
-            python2.7 -m pip install taskcluster &&
-            python2.7 decision-task.py
+            python2.7 decision-task/run.py

decision-task/requirements.txt

@@ -0,0 +1 @@
+taskcluster==4.0.1

decision-task/run.py

@@ -1,6 +1,10 @@
 # coding: utf8
 
 import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "vendored"))
+
 import json
 import taskcluster
 

decision-task/vendor.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+cd $(dirname $0)
+python2 -m pip install -r requirements.txt --target vendored