Added libprocess and stout to doxyfile.

Previously, we only scanned src/ and include/. This patch adds
3rdparty/libprocess/src, 3rdparty/libprocess/include and
3rdparty/libprocess/3rdparty/stout.

Review: https://reviews.apache.org/r/24481
Modified the default for ephemeral ports per container.

Review: https://reviews.apache.org/r/24461
Temporarily disabled HealthcheckTest.ConsecutiveFailures test due to
MESOS-1613.