OPENAFS-SA-2018-001 Add auditing to butc server RPC implementations

OPENAFS-SA-2018-001 Add auditing to butc server RPC implementations

Make the actual implementations into helper functions, with the RPC
stubs calling the helpers and doing the auditing on the results, akin
to most other server programs in the tree.  This relies on support for
some additional types having been added to the audit framework.

Change-Id: Ic872d6dfc7854fa28bd3dc2277e92c7919d0d0c0