Refactor some daemon code to facilitate the introductioin of static
probes, sanitizing function exit paths in many places

* daemon/libvirtd.c: Pass the dname string into remoteCheckDN
  to let caller deal with failure paths. Add separate exit paths
  to remoteCheckCertificate for auth failure vs denial. Merge
  all exit paths in qemudDispatchServer to one cleanup block
* daemon/remote.c: Add separate exit paths to SASL & PolicyKit
  functions for auth failure vs denial