Removed bin/mesos-build-env.sh.in in favor of just putting flags in
the bin/mesos-master.sh.in, bin/mesos-slave.sh.in, and
bin/mesos-local.sh.in scripts since some binaries require different
flags and they will fail on startup if they try and load an unknown
flag.

Review: https://reviews.apache.org/r/12118
Moved master/slave HTTP route handlers into inner class.

Review: https://reviews.apache.org/r/12119
Added help pages to libprocess.

Review: https://reviews.apache.org/r/11710
Updated routes in Mesos to provide help.

Review: https://reviews.apache.org/r/12120
Refactored HierarchicalAllocatorProcess to use roles instead of users.

Review: https://reviews.apache.org/r/11205/