add authenticated docker pulls

Author: harryturr

.circleci/config.yml

@@ -4,6 +4,9 @@ jobs:
     python-3.6: &test-template
         docker:
             - image: circleci/python:3.6-stretch-node-browsers
+              auth:
+                username: dashautomation
+                password: $DASH_PAT_DOCKERHUB
 
         environment:
             PERCY_ENABLE: 0
@@ -46,10 +49,16 @@ jobs:
         <<: *test-template
         docker:
             - image: circleci/python:2.7-stretch-node-browsers
+              auth:
+                username: dashautomation
+                password: $DASH_PAT_DOCKERHUB
 
     python-3.7-install-test:
         docker:
             - image: circleci/python:3.7-stretch-node-browsers
+              auth:
+                username: dashautomation
+                password: $DASH_PAT_DOCKERHUB
 
         environment:
             PERCY_ENABLE: 0
@@ -101,6 +110,9 @@ workflows:
     version: 2
     build:
         jobs:
-            - python-3.6
-            - python-2.7
-            - python-3.7-install-test
+            - python-3.6:
+                context: dash-docker-hub
+            - python-2.7:
+                context: dash-docker-hub
+            - python-3.7-install-test:
+                context: dash-docker-hub