Improve documentation of (unpin|pin)_cpus_with_siblings()
Improve documentation of (unpin|pin)_cpus_with_siblings()

Those two methods require some thought to understand, try to make it
easier by adding docstrings and comments.

Change-Id: I1cc304051e36eff8128c14c5d2398f6c311f0cef

openstack/nova,klmitch/nova,mahak/nova,klmitch/nova,mahak/nova,klmitch/nova,openstack/nova,openstack/nova,mahak/nova,klmitch/nova