Add a REST enpoint to abort a command

The use cases are:

• abort a very long command run by mistake
• abort a command that is in error and that blocks other commands on the same action

A command in error is a possible case when:

• The action doesn't respect their contract:
  • stop on an error that should be expected (like the user doesn't have enough permission)
  • doesn't validate its parameters and invalid input generates an error
  • don't report enough processed documents and stay in running state (this is not a blocking case)
• The KV store has been flushed and action and status computation cannot found command or status.

Being able to cancel a command providing its identifier will enable to recover from such situation.

Possible implementation:

• a bulk service abort method will set the status of the command to something like ABORTED
• AbstractBulkComputation when not able to retrieve the command will check its status, in case of abort we skip the record instead of terminating in error
• BulkStatusComputation will simply ignore record with the ABORTED status
• the bulk service await should return true on aborted command

Depending on when the command has been aborted, we can have:

• a completed command because the abort is receive after the completion
• a complete cancelation of the command if the action has not been applied on any document
• a partial command where a part of the document set has been processed

The status is written to the done stream as way to give feedback on downstream processing.

A possible rest endpoint can be:

curl -s -X PUT "http://localhost:8080/nuxeo/api/v1/bulk/$commandId/abort"  -u Administrator:Administrator  -H 'content-type: application/json' 
# returns the status so we know if the command has been ABORTED or if it is already COMPLETED