Use 4 nodes for sanity tests in CI.

shippable.yml

@@ -11,6 +11,7 @@ matrix:
     - env: T=sanity/1
     - env: T=sanity/2
     - env: T=sanity/3
+    - env: T=sanity/4
 
     - env: T=units/2.6
     - env: T=units/2.7

test/utils/shippable/sanity.sh

@@ -17,8 +17,9 @@ fi
 
 case "${group}" in
     1) options=(--skip-test pylint --skip-test ansible-doc --skip-test docs-build) ;;
-    2) options=(--test pylint) ;;
+    2) options=(--test ansible-doc --test docs-build) ;;
-    3) options=(--test ansible-doc --test docs-build) ;;
+    3) options=(--test pylint --exclude test/units/ --exclude lib/ansible/module_utils/ --exclude lib/ansible/modules/network/) ;;
+    4) options=(--test pylint           test/units/           lib/ansible/module_utils/           lib/ansible/modules/network/) ;;
 esac
 
 # shellcheck disable=SC2086