Remove --without-cxx11 flag

C++11 is required now. Specifying this flag makes no change in the actual compilation of mesos.

Review: https://reviews.apache.org/r/26724
Delete framework data in TaskStatus to avoid OOM

There was a bug found that Spark use TaskStatus.data to transfer computed
result and mesos-master RES memory keeps increasing fast and finally will be
killed by OOM killer.

Review: https://reviews.apache.org/r/25184
Minor style fix from https://reviews.apache.org/r/25184/
Added --modules flag for Mesos slave.

Review: https://reviews.apache.org/r/26509
Replaced cerr/exit with EXIT when parsing master flags.

Review: https://reviews.apache.org/r/26629
Fixed minor typos in configure.ac.

Review: https://reviews.apache.org/r/26728
Added DISTRIBUTE reference so that protobuf egg can be built locally.

Review: https://reviews.apache.org/r/26788
Expose poll interval from the reaper.

Review: https://reviews.apache.org/r/26229
Installed mesos pre commit hook and .gitignore on bootstrap.

Review: https://reviews.apache.org/r/26794
First try to fix #1571. Propagate shutdown timeout to Executor and CommandExecutor via env variable. Remove escalation constant for command executor.
Second try to fix 1571.
Third try to fix 1571. Move shutdown adjust timeout logics into utility function, improve comments and style.
Fix build errors.
Add a comment about ShutdownProcess design.
Add tests for graceful shutdown.
Add and fix comments.
Fix graceful shutdown test on Linux.
Add more comments.
Update comments.
Rename functions adjusting timeouts; introduce a check; update comments.