Turn 'check_who' into a decorator
Turn 'check_who' into a decorator

This helper function seems to be more pretty/nice as
a decorator that is used uniformly instead of repeated
calling into it from needed functions.

Change-Id: If8aa2fb914cf80fdcecc37f044ab129d13f12be8

jimbobhickville/taskflow,junneyang/taskflow,pombredanne/taskflow-1,openstack/taskflow,openstack/taskflow,jimbobhickville/taskflow,pombredanne/taskflow-1,junneyang/taskflow