The number of current pending tasks is useful to detect and overloaded master. This commit adds it to the cluster health API. The complete list can be retrieved from the dedicated pending tasks API.
It also adds rest tests for the cluster health variants.
Closes#9877
The description of the timeout parameter was worded misleadingly; it implied that the API would wait until the cluster reached the desired level and then stayed at that level for the timeout. I've tweaked the sentence to remove the risk of confusion.
Boaz Leskes
Clinton Gormley
Richard Boulton
Lee Hinman