Merge resourcesRecovered and resourcesUnused.

Review: https://reviews.apache.org/r/24331
Added executor metrics for slave.

Review: https://reviews.apache.org/r/24124
Changed socket closed while receiving to VLOG(2).
Fixed two flaky tests in AllocatorTest.

Review: https://reviews.apache.org/r/24418
MESOS-1170 Unbundle glog

Enable mesos to build against the system installed version of glog.

Review: https://reviews.apache.org/r/23453
Checked docker validation status code.

Review: https://reviews.apache.org/r/24419
Fixed mesos-style.py errors.
Re-enabled low level scheduler tests.
Made doxygen recursive to include nested files.

Running doxygen without the 'recursive' flag enable didn't capture any
source or include files as we only point to include/ and src/.

Review: https://reviews.apache.org/r/24430
Added 'process::inject::exited()' to simulate exited events in tests.

Review: https://reviews.apache.org/r/20504
Improved framework rate limiting by imposing the max number of outstanding messages per framework principal.

Review: https://reviews.apache.org/r/24343
Fixed a bug in slave when launching container.

Review: https://reviews.apache.org/r/24440
Reverted a refactor that broke the build.
Add ContainerInfo and Volumes proto defs

Review: https://reviews.apache.org/r/24349