Handle missing shortNames


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13680 e27351fd-9f3e-4f54-a53b-843176b1656c
When converting resources.xml, retain <guid> element


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13681 e27351fd-9f3e-4f54-a53b-843176b1656c
If no args are passed, use a single invocation of trial rather than a loop


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13682 e27351fd-9f3e-4f54-a53b-843176b1656c
Groups' disappearance from the directory affects their extant value


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13683 e27351fd-9f3e-4f54-a53b-843176b1656c