qemu: only report errno in trace message on failure
qemu: only report errno in trace message on failure

Avoid reporting a stale errno value when the syscall succeeds,
instead always pass 0.

Signed-off-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

fabianfreyer/libvirt,eskultety/libvirt,VenkatDatta/libvirt,taget/libvirt,libvirt/libvirt,libvirt/libvirt,jfehlig/libvirt,datto/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,taget/libvirt,taget/libvirt,datto/libvirt,eskultety/libvirt,datto/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,taget/libvirt,jardasgit/libvirt,taget/libvirt,crobinso/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,nertpinx/libvirt,olafhering/libvirt,jardasgit/libvirt,libvirt/libvirt,eskultety/libvirt,jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,datto/libvirt,zippy2/libvirt,jardasgit/libvirt,olafhering/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,crobinso/libvirt,zippy2/libvirt,eskultety/libvirt,andreabolognani/libvirt,eskultety/libvirt,zippy2/libvirt,fabianfreyer/libvirt,datto/libvirt,jardasgit/libvirt,crobinso/libvirt,libvirt/libvirt,VenkatDatta/libvirt,crobinso/libvirt