Revert "Switched to subprocess.Popen to get stdout streamed from"

This reverts commit 7013f47c3b59314db2b560d67edf1d01afd4a2db.
Updates Mesos version in Getting Started guide to 0.19.0
Simplifies documentation headers.
Added infix operator for IntervalSet.

Review: https://reviews.apache.org/r/22444
Fixed child process leaks in SlaveRecoveryTest.GCExecutor.
Updated verify-reviews to catch exceptions during cleanup.
Cleanly exit a forked executor if the slave terminates during launch.

Review: https://reviews.apache.org/r/22481
Fixed a flaky test: SlaveTest.TerminatingSlaveDoesNotReregister.

Review: https://reviews.apache.org/r/22472
Fixed ZooKeeperProcess and ProcessWatcher to avoid deadlock during ZooKeeperProcess termination.

Review: https://reviews.apache.org/r/22521
Fixed SlaveRecoveryTest.RestartBeforeContainerizerLaunch test.

Review: https://reviews.apache.org/r/22441
Removed TODO that was done.

Review: https://reviews.apache.org/r/22577
Added grace period to health check and moved health check into TaskInfo.

Review: https://reviews.apache.org/r/22519
Fixed typo in health check grace periods field.

Review: https://reviews.apache.org/r/22589
Make unknown container not a Failure for Isolator::cleanup.

Review: https://reviews.apache.org/r/22049
Add a cgroup perf_event isolator.

This isolator only creates the perf_event cgroup and places the executor
into the cgroup; no performance statistics are gathered/exported.

Review: https://reviews.apache.org/r/20963
Introduce a PerfStatistics protobuf.

Review: https://reviews.apache.org/r/21442
Support for running "perf stat".

Perf can be run against either a set of pids or a set of perf_event cgroups.

Review: https://reviews.apache.org/r/21443
Add sampling support to the perf_event isolator.

Review: https://reviews.apache.org/r/21451
Verbose Maven configure error.

Review: https://reviews.apache.org/r/21950
Adding missing files to gitignore template.

Review: https://reviews.apache.org/r/21718