Downgrade from Mesos 0.20+ back to Mesos 0.18.2
(reverted parts of commits from
https://github.com/airbnb/chronos/commit/1961c37a65f4077055faee9b8ebdb3cd9efed2f4#diff-600376dffeb79835ede4a0b285078036)

WARNING: the UI may indicate that Docker support is available, however,
it shall be ignored!

Why the downgrade? Because AMPLAB Spark 1.1 only supports running on
Mesos 0.18.2 :(

TBD: downgrade other Mesos 0.20+ specific code