.gitignore: Filter out the nested .kube cache

This directory is populating when the e2e suite is supplied with an output $ARTIFACTS_DIR, and the script that's responsible for gathering CI testing artifacts when a test case fails.

Signed-off-by: timflannagan <[email protected]>

Author: timflannagan

Diff for: .gitignore

@@ -455,5 +455,5 @@ apiserver.key
 
 !vendor/**
 test/e2e-local.image.tar
-
+test/e2e/.kube
 dist/