CA-125868: Return the task for a wait asynchronously

Xenopsd uses this task to schedule a timeout on a watch. We need to make
sure this call doesn't block before returning the task.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #4 from simonjbeaumont/ca-125868

CA-125868: Return the task for a wait asynchronously