Travis_wait flaky on ppc64le at travis-ci.com

Job failed on ppc64le due to 10 minutes no output despite using travis_wait

Job links:
https://travis-ci.com/github/IBM/powerai/jobs/323902212
https://travis-ci.com/github/IBM/powerai/jobs/334985397

The failure is flaky and is mostly observed for conda-forge packages at travis-ci.com.

Don’t send travis_wait … to the background.

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