qemu-img: Add "Quiet mode" option

There can be a need to turn output to stdout off. This patch adds a -q option
that enable "Quiet mode". In Quiet mode, only errors are printed out.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/qemu-img.texi b/qemu-img.texi
index 1a6c9e3..43430fb 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -54,6 +54,9 @@
 with or without a command shows help and lists the supported formats
 @item -p
 display progress bar (convert and rebase commands only)
+@item -q
+Quiet mode - do not print any output (except errors). There's no progress bar
+in case both @var{-q} and @var{-p} options are used.
 @item -S @var{size}
 indicates the consecutive number of bytes that must contain only zeros
 for qemu-img to create a sparse image during conversion. This value is rounded