virStream*All: Preserve reported error

virStream*All: Preserve reported error

If one these four functions fail (virStreamRecvAll,
virStreamSendAll, virStreamSparseRecvAll, virStreamSparseSendAll)
the stream is aborted by calling virStreamAbort(). This is  a
public API; therefore, the first thing it does is error reset. At
that point any error that caused us to abort stream in the first
place is gone.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>