Fixed exception tests to use the latest test abstractions.

From: Jiang Yan Xu <yan@jxu.me>
Review: https://reviews.apache.org/r/10318

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1467417 13f79535-47bb-0310-9956-ffa450edef68
Fixed Allocator Test to use DROP_MESSAGE, FutureArg, moved
expectations closer to actions, etc. Additionally, replaced the
MockAllocator in DRFAllocatorTest with a regular Allocator because the
expectations were uninteresting, expectations on calls to the
allocator are covered in other tests, and it just made the test a lot
messier.

From: Thomas Marshall <twm378@gmail.com>
Review: https://reviews.apache.org/r/10329

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1467418 13f79535-47bb-0310-9956-ffa450edef68
Fixed AllocatorZookeeperTest to use latest abstractions. Removed
triggers, updates EXPECT_MESSAGE logic, and moves EXPECT_CALLs closer
to actions.

From: Thomas Marshall <twm378@gmail.com>
Review: https://reviews.apache.org/r/10386

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1467419 13f79535-47bb-0310-9956-ffa450edef68