Fixed flaky SlaveTest.KillTaskBetweenRunTaskParts test.

Moving EXPECT_CALL(removeFramework) before killTask() removes a race,
which made the expected call occur before it is expected.

Review: https://reviews.apache.org/r/26929
Split authorization from task validation.

Review: https://reviews.apache.org/r/26817
Add dispatch event counters to Scheduler driver

Review: https://reviews.apache.org/r/26951
Added a document for reconciliation.

Review: https://reviews.apache.org/r/26669
Added reconciliation to the documentation home.

Review: https://reviews.apache.org/r/26670
Fix containerizer not receiving destroy/update calls when launching.

Review: https://reviews.apache.org/r/26486