Bump instance updated_at on network change.

Update add-fixed-ip and remove-fixed-ip code paths to update the
updated_at field of the instance, since from the user's perspective
through the API, they have made a change to the instance's
configuration.  In that case, it makes sense to expect that the
updated_at field gets changed.

Fix bug 1143466.

Change-Id: Icfd7d0b1b556795d94a22c1719727f8c9fc744f0
Put options in a list.

Update nova.notifications configuration options to be in a list, like
pretty much everywhere else.  For some reason when I saw this it buged
me so ... I changed it.

Change-Id: I551aba4eaceed2d1a8925e9ab621a030af83eeca
Merge "Bump instance updated_at on network change."
Merge "Put options in a list."