Make Instance.save() log missing save handlers

Also, fix the name of the _save_fault() handler to be what it should
be, which is what triggered the ungraceful handling of this bug in
the first place.

Change-Id: I160f42b130810134135d2a22198fc0b66a7af585
Closes-bug: 1223957
Merge "Make Instance.save() log missing save handlers"