ci: Split building and waiting for base image into its own command

This should help reduce the overall time associated with the test step
and avoid reaching the 120mins cutoff time for a given command.

circle.yml

@@ -17,6 +17,10 @@ dependencies:
 
 test:
   override:
+    - circleci-matrix:
+        parallel: true
+        environment:
+          STEP: dependencies
     - circleci-matrix:
         parallel: true
         timeout: 3000