Adjust async poll timeout
Adjust async poll timeout

If the storage service is busy running background tasks, a poll event
might take a little more than 5 seconds to return, and that's not
really a problem.  Wait a bit longer instead of aborting straight
away.

Addresses https://github.com/archivematica/Issues/issues/114.

artefactual/archivematica,artefactual/archivematica,artefactual/archivematica,artefactual/archivematica