Make port group changes more robust
Make port group changes more robust

port_group_name and port_group_id cannot be non-NULL at the same time.
Make the update code more robust in case the wrong one of the two was
set in the past.

Change-Id: Ic7f6e9c498f83d83d47c5e0fa8f97c59adfdbcbb
Reviewed-by: Priya Joshi <3c6cfa6f57440adfc837c4ad04483313acbc2582@morganstanley.com>

quattor/aquilon,quattor/aquilon,guillaume-philippon/aquilon,quattor/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon