Fix LDAP group modification changes via the CLI.

The XML-RPC interface for group modification didn't consider the special
restrictions for LDAP groups. This patch adds that.

Bug: 972255
Display error message when job cannot be cancelled.

Bug: 972290
Change-Id: I534b5dd666e732af07d4b02aab27c71197df4f24
Automatic commit of package [beaker] release [0.13.0-3].