qerror: add qerror_report_err()

This provides a bridge between Error (new error mechanism) and QError (old error
mechanism).  Errors can be propagated whereas QError cannot.

The minor evilness avoids layering violations.  Since QError should go away RSN,
it seems like a reasonable hack.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
