SPARK-1806 (addendum) Use non-deprecated methods in Mesos 0.18

The update to Mesos 0.18 caused some deprecation warnings in the build. The change to the non-deprecated version is straightforward as it emulates what the Mesos driver does with the deprecated method anyway (https://github.com/apache/mesos/blob/c5aa1dd22155d79c5a7c33076319299a40fd63b3/src/sched/sched.cpp#L1354)

Author: Sean Owen <sowen@cloudera.com>

Closes #920 from srowen/SPARK-1806 and squashes the following commits:

8d76b6a [Sean Owen] Use non-deprecated methods in Mesos 0.18