introduced NodeSettingsSource in the test infrastructure os tests with scopes TEST & SUITE without an explicit numNodes definitions will fall back on the nodeSettings(int) callback
Returning useful exception when sorting on a completion field

Closes #3747
added a ToXContent implementation to NodeStats
cleanup testcase
Expose several options from MockDirWrapper via index settings

Index settings can now override default behavior for 'double write'
and 'no delete open files' on MockDirectoryWrapper if tests use these
options in a legit. way. ie. in a restore situation a double write
is a legit operation.
Move Mock Store impls to test package
Added generic cluster state update ack mechanism

Added new AckedClusterStateUpdateTask interface that can be used to submit cluster state update tasks and allows actions to be notified back when a set of (configurable) nodes have acknowledged the cluster state update. Supports a configurable timeout, so that we wait for acknowledgement for a limited amount of time (will be provided in the request as it curently happens, default 10s).

Internally, a low level AckListener is created (InternalClusterService) and passed to the publish method, so that it can be notified whenever each node responds to the publish request. Once all the expected nodes have responded or the timeoeout has expired, the AckListener notifies the action which will return adding the proper acknowledged flag to the response.

Ideally, this new mechanism will gradually replace the existing ones based on custom endpoints and notifications (per api).

Closes #3786