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.

.circleci-matrix.yml

@@ -14,7 +14,7 @@ env:
   - IMAGE=windows-x86
 command:
   - |
-    if [[ $STEP == "test" ]]; then
+    if [[ $STEP == "dependencies" ]]; then
       if [[ $CIRCLE_NODE_INDEX == 0 ]]; then
         if [[ ! -f ~/BASE_AVAILABLE ]]; then
           if [[ -e ~/docker/base.tar ]]; then time docker load -i ~/docker/base.tar; fi
@@ -42,6 +42,8 @@ command:
           echo "Base image already downloaded"
         fi
       fi
+    fi
+    if [[ $STEP == "test" ]]; then
       if [[ -e ~/docker/$IMAGE.tar ]]; then time docker load -i ~/docker/$IMAGE.tar; fi
       time docker pull dockcross/$IMAGE
       time docker load -i ~/docker/base.tar

circle.yml

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