Add agent request cancellation plumbing.
Add cancel support to content itineraries.
Add cancelled() to the handler conduit.
Merge branch 'master' into jortel-cancel-agent-requests
Merge branch 'master' into jortel-cancel-agent-requests
use task cancel_hook instead of the lifecycle hook.
 no timeout on cancel request.
Merge branch 'master' into jortel-cancel-agent-requests
 no timeout on cancel request (hub).
update requires gofer >= 0.76 which provides cancellation support.
async timeout defaults to None.
Merge pull request #464 from pulp/jortel-cancel-agent-requests

Jortel cancel agent requests