gitlab-ci: Automatically retry jobs after runner system failure

Up to twice, for a total of 3 attempts maximum.

This will hopefully avoid spurious CI pipeline failures due to
intermittent GitLab/docker infrastructure issues.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 5e15f1e..87968b6 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -31,6 +31,10 @@
     - master
     - merge_requests
     - /^ci([-/].*)?$/
+  retry:
+    max: 2
+    when:
+      - runner_system_failure
 
 
 # CONTAINERS