Added stream operator for filter::ip::PortRange.

Review: https://reviews.apache.org/r/21505
MESOS-1376: Fixed an invalid reference in the Registrar.
Added backoff to slave's initial (re-)registration attempt.

Review: https://reviews.apache.org/r/21464
Set work_dir flag for mesos-local.

Review: https://reviews.apache.org/r/21562
Fixed invalid comment string in slave.cpp