Rationale:
We use --quiet mode when testing a PR in the CI. Also, we use `stamp` to
prefix every line with a timestamp. Previously, when testing in --quiet
mode, we will only print a dot for each test without any line breaks.
Combined with `stamp`, this means we'd need to wait for all tests to
complete before writing the output. On Travis CI, if we don't print
anything within 30 minutes, the job will be forcefully canceled. This
makes it very easy to spuriously-timeout when testing non-default images
like arm-android using the CI. This commit tries to workaround the issue
by printing a new line every 100 dots, forcing `stamp` to emit something
to reset Travis's countdown.
a4e5c91cb8