Added DISCLAIMER to the distribution.

Review: https://reviews.apache.org/r/11463
Fixed bug where gtest filter wasn't properly being setup for tests.

Review: https://reviews.apache.org/r/9798

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1454139 13f79535-47bb-0310-9956-ffa450edef68
*** Modified for 0.12.0 *** Fixed release script to use git instead of svn.
Added CHANGELOG, Upgrades, Master Detection documents for 0.12.0.
*** Modified for 0.12.0 *** Updated the NOTICE to include the correct year, and to fix line wrapping.
*** Modified for 0.12.0 *** Updated LICENSE for 0.12.0.
Updated release tag format in the release script to use the new 0.12.0-rc1 style formatting.

Review: https://reviews.apache.org/r/11786