Small cleanups of the Master code.

Review: https://reviews.apache.org/r/15114
Added an example java log test.

Review: https://reviews.apache.org/r/17780
Added valgrind runnables.

Adds valgrind runnables for executing memory / leak checks on mesos.
The runnables accept an additional parameter (-t) for selecting a
valgrind tool. The default (no option given) is memcheck. All other
parameters are passed on to the given target (master, slave, tests,
local).

Example: build/bin/valgrind-mesos-tests.sh -t helgrind

Review: https://reviews.apache.org/r/17636
Added a log tool to start a replica server.

Review: https://reviews.apache.org/r/17755
Added a log tool that does performance tests on the log.

Review: https://reviews.apache.org/r/17767
Added observe endpoint to master.

This changes adds a new HTTP endpoint of observe to master.
This allows clients to report health via an HTTP POST.
Values are:
   MONITOR = Monitor for which health is being reported.
   HOSTS = Comma seperated list of hosts.
   LEVEL = OK for healthy, anything else for unhealthy.

This also contains a small fix to alphabetize the existing
endpoints / help strings.

Review: https://reviews.apache.org/r/17255