This patch adds partial support for running spark on mesos inside of a docker container. Only fine-grained mode is presently supported, and there is no checking done to ensure that the version of libmesos is recent enough to have a DockerInfo structure in the protobuf (other than pinning a mesos version in the pom.xml).

Author: Chris Heller <hellertime@gmail.com>

Closes #3074 from hellertime/SPARK-2691 and squashes the following commits:

d504af6 [Chris Heller] Assist type inference
f64885d [Chris Heller] Fix errant line length
17c41c0 [Chris Heller] Base Dockerfile on mesosphere/mesos image
8aebda4 [Chris Heller] Simplfy Docker image docs
1ae7f4f [Chris Heller] Style points
974bd56 [Chris Heller] Convert map to flatMap
5d8bdf7 [Chris Heller] Factor out the DockerInfo construction.
7b75a3d [Chris Heller] Align to styleguide
80108e7 [Chris Heller] Bend to the will of RAT
ba77056 [Chris Heller] Explicit RAT exclude
abda5e5 [Chris Heller] Wildcard .rat-excludes
2f2873c [Chris Heller] Exclude spark-mesos from RAT
a589a5b [Chris Heller] Add example Dockerfile
b6825ce [Chris Heller] Remove use of EasyMock
eae1b86 [Chris Heller] Move properties under 'spark.mesos.'
c184d00 [Chris Heller] Use map on Option to be consistent with non-coarse code
fb9501a [Chris Heller] Bumped mesos version to current release
fa11879 [Chris Heller] Add listenerBus to EasyMock
882151e [Chris Heller] Changes to scala style
b22d42d [Chris Heller] Exclude template from RAT
db536cf [Chris Heller] Remove unneeded mocks
dea1bd5 [Chris Heller] Force default protocol
7dac042 [Chris Heller] Add test for DockerInfo
5456c0c [Chris Heller] Adjust syntax style
521c194 [Chris Heller] Adjust version info
6e38f70 [Chris Heller] Document Mesos Docker properties
29572ab [Chris Heller] Support all DockerInfo fields
b8c0dea [Chris Heller] Support for mesos DockerInfo in coarse-mode.
482a9fd [Chris Heller] Support for mesos DockerInfo in fine-grained mode.