Added abstraction for resources transformation.

Review: https://reviews.apache.org/r/29018
Added a Resources transformation for acquiring persistent disk.

Review: https://reviews.apache.org/r/29128
Fixed a compilation issue on gcc 4.4.7.
Removed an unnecessary helper in the sorter tests.

Review: https://reviews.apache.org/r/29088
Fixed the DRFSorter share calculation to not assume flattened resources.

Review: https://reviews.apache.org/r/29089
Temporarily disabled health check test.

Health check test is flaky and has been temporarily disabled until we
have found the root cause.
Updated Sorter to allow transforming allocated resources.

Review: https://reviews.apache.org/r/29083
Updated Allocator to allow transforming allocated resources.

Review: https://reviews.apache.org/r/29084
Added an overload of Resources::contains for Resource object.

Review: https://reviews.apache.org/r/29134
Added a method in Resources to return all persistent disks.

Review: https://reviews.apache.org/r/29177
Disallowed empty DiskInfo.

Review: https://reviews.apache.org/r/29178
Renamed totalResources in master to offeredResources.

Review: https://reviews.apache.org/r/29179
Adjusted the calculation of unused resources in _launchTasks by
considering persistent disk acquisition.

Review: https://reviews.apache.org/r/28720
Add slave id to docker container name prefix.
Add option to disable docker containerizer killing orphans
Add executor for docker containerizer
Integrate docker executor into containerizer.
Re-enable docker recover test.
Add docker_mesos_image flag to slave flags.
Add docker_sock to slave flags