Tests: Reduce runtime for high_throughput_limits test

Tests: Reduce runtime for high_throughput_limits test

The test currently takes about 2 hours to run. The iteration count and
range of bandwidth limits have been adjusted to reduce the runtime,
while hopefully covering the same goal: attempting to catch rare race
conditions in low-bandwidth scenarios.

The iteration count has been set so there should be some dropped
events, and a diagnostic message emitted if ever there are no dropped
events.

Change-Id: I670414b60c6881c3a6f7aafd2c1b0c4540e6707f
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>