Add docstring describing the inject instance variable
Add docstring describing the inject instance variable

Change-Id: I00c48fc6a5f579fe72badc034fbd293f2eb41d5c

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