* Initial commit of rest high level exposure of cancel task
* fix javadocs
* address some code review comments
* update branch to use tasks namespace instead of cluster
* High-level client: list tasks failure to not lose nodeId
This commit reworks testing for `ListTasksResponse` so that random
fields insertion can be tested and xcontent equivalence can be checked
too. Proper exclusions need to be configured, and failures need to be
tested separately. This helped finding a little problem, whenever there
is a node failure returned, the nodeId was lost as it was never printed
out as part of the exception toXContent.
* added comment
* merge from master
* re-work CancelTasksResponseTests to separate XContent failure cases from non-failure cases
* remove duplication of logic in parser creation
* code review changes
* refactor TasksClient to support RequestOptions
* add tests for parent task id
* address final PR review comments, mostly formatting and such
Paul Sanwald