[autotest] Add retry to `ps` in drone_utility.

We're seeing the ps invocation fail due to a segfault, so let's add a
few retries for happiness.

BUG=chromium:310699
TEST=ran locally with desktop as remote drone

Change-Id: Ia6c829e136e22667cc17705df58994b78a8cb617
Reviewed-on: https://chromium-review.googlesource.com/174532
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
1 file changed