na: add travis_wait to CI
na: add travis_wait to CI

Travis CI is erroring out because it does not receive STDOUT
for 10m. This may be because some test suites take a while
to run (note that output is buffered per suite of test; we
do not get output per test).

This CL adds the travis_wait command in front of the
run-tests invocation, extending the time from 10m to 20m.

This CL is experimental and may not fix the issue, but even
if this does not fix our tests we'll have a better idea of
whether it's a not-enough-time issue or an actually-hanging
issue.

https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

Change-Id: I0ce07b6fc50843162add4d7f880c5d80976a094b
Reviewed-on: https://code-review.googlesource.com/33053
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go