Allow to provide a list of uuids for rally task delete

Task delete command now accept a list of uuids :
  rally task delete --force --uuid uuid_1 uuid_2 uuid_3
Previous usages are still available:
  rally task delete --force
  rally task delete --force task_uuid
  rally task delete --force --uuid task_uuid

Change-Id: I85a6225476dab3ff27718d3dadf73810f8da3ebf
Merge "Allow to provide a list of uuids for rally task delete"