add portgroups in the task_manager docstrings
add portgroups in the task_manager docstrings

Ironic portgroup property is added to the TaskManager class,but it is 
not mentioned in the docstrings..

Change-Id: I228fd3410810b130d14d8c53cf14eade5186153d

pshchelo/ironic,openstack/ironic,openstack/ironic,SauloAislan/ironic,SauloAislan/ironic,pshchelo/ironic