separate and isolate linux_host admin RPC stubs

The client and server stub code for linux_host admin RPC calls is very
boring and repetitive. On the client side, take the real args, pack
them in protobufs, invoke rpc.Call, unpack results and return them. On
the server side, take the packed args, unpack them, call the real
function, then pack the results into a protobuf.

This patch moves all such code for linux_host admin RPCs into a
separate file. Ideally, that file could be auto-generated based on,
say, an interface definition (and maybe a mapping to protobuf fields,
or just generate the protobuf automatically). Until then, a separate
file for this boring stuff keeps the actual, interesting linux_host
logic cleaner.
separate and isolate linux_host Tao RPC stubs

Rename files and cleanup linux_host server stub code to match the
admin stub code.  Also properly use protorpc for these stubs. Get rid
of the "handle" prefix on functions in LinuxHost.
fix TaoRPC when nil issuer; all tests pass
fix issues from rpc_cleanup.diff
response to auth_integration.diff
remove stale author lines