CI: use travis_wait to avoid build timeouts

[mwtoews]

Commands that take longer than 10 minutes on TravisCI raise a timeout error:

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

The suggested solution is to prefix the long-running command with travis_wait or travis_wait n, where n is the number of minutes, with a default of 20 mins.

Another question is if Travis CI builds are recently taking longer than 10 minutes? These errors started around 2 weeks ago.

[mwtoews]

Hum, this PR is probably not going to fix it, as the error still happens.

Is the issue related to changes with s390x? Update: a possible TravisCI issue described here.

[rouault]

yes I already reaches Travis CI support on July 31st for the same issue on GDAL, and still waiting for a fix