Prevent random build failures

Looks like some odd race condition causes failed builds by attempting to
run the task that should be disabled.
Disable the task explicitly untill we figure it out.

x-pack/test/smb-fixture/build.gradle

@@ -1,2 +1,5 @@
 apply plugin: 'elasticsearch.build'
 apply plugin: 'elasticsearch.test.fixtures'
+
+// TODO: elasticsearch.test.fixtures should disable this but it sometimes doesn't
+jarHell.enabled  = false