Revert "Upgrade CircleCI executor"

This reverts commit 3c996ac.

Author: 2opremio

.circleci/config.yml

@@ -2,8 +2,7 @@ version: 2
 jobs:
   make-eksctl-image:
     # use machine build, as otherwise we cannot use make and have to duplicate makefile
-    machine:
-      image: ubuntu-1604:201903-01
+    machine: true
     steps:
       - checkout
       - run: mkdir -p ./test-results/ginkgo