Remove hack using existance of an 'identity' string to disable auth

Remove hack using existance of an 'identity' string to disable auth

Currently the server determines whether authentication of clients
is complete, by checking whether an identity is set. This patch
removes that lame hack and replaces it with an explicit method
for changing the client auth code

* daemon/remote.c: Update for new APis
* src/libvirt_private.syms, src/rpc/virnetserverclient.c,
  src/rpc/virnetserverclient.h: Remove virNetServerClientGetIdentity
  and virNetServerClientSetIdentity, adding a new method
  virNetServerClientSetAuth.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>