Updated documentation/flags regarding new default hostname semantics.

Review: https://reviews.apache.org/r/26185
Synced container network configurations with host network
configurations.

Review: https://reviews.apache.org/r/26197
Changed routing diagnosis socket state from enum to int so that they can
be bitwiseor'ed together.

Review: https://reviews.apache.org/r/26236
Included a missing header file in src/Makefile.am.
Fixed the flaky SlaveRecoverTest.MultipleSlaves.

Review: https://reviews.apache.org/r/26243
Switched path::join() to be variadic

Review: https://reviews.apache.org/r/25818
MESOS-1857 Fixed path::join() on older libstdc++ which lack back().

Review: https://reviews.apache.org/r/26256
Added webui_url to FrameworkInfo and web UI.

Allows frameworks to register a URL to its web UI.

Review: https://reviews.apache.org/r/26125
Replace some asserts with CHECKs in dispatch.

Review:
Added TCP RTT statistics for port mapping network isolator.

Review: https://reviews.apache.org/r/26090
Converted diagnosis socket Info to a struct.

Review: https://reviews.apache.org/r/26290
Moved Mesos version from mesos.hpp to version.hpp.

This allows the Module subsystem to simply include <mesos/version.hpp>
instead of inheriting the whole protobuf header chain.

Review: https://reviews.apache.org/r/26303