[travis] detect errors in docker test
[travis] detect errors in docker test

Summary:
As noticed by technion in https://github.com/facebook/infer/issues/570,
failures in the Docker test do not result in failures of the test. Lol.

Reviewed By: mbouaziz

Differential Revision: D4605364

fbshipit-source-id: de9f84c

blzq/infer,blzq/infer,blzq/infer,jsachs/infer,ryoon/infer,ropas/infer,ropas/infer,facebook/infer,jvillard/infer,jsachs/infer,ryoon/infer,jvillard/infer,blzq/infer,ropas/infer,blzq/infer,jsachs/infer,facebook/infer,ropas/infer,facebook/infer,facebook/infer,ropas/infer,jsachs/infer,jsachs/infer,facebook/infer,ryoon/infer,blzq/infer,jvillard/infer,ryoon/infer,jvillard/infer,jvillard/infer,jvillard/infer,jsachs/infer,facebook/infer,ropas/infer,facebook/infer,ryoon/infer,jvillard/infer,ryoon/infer