qemu-img: add the 'dd' subcommand

This patch adds a basic dd subcommand analogous to dd(1) to qemu-img.

For the start, this implements the bs, if, of and count options and requires
both if and of to be specified (no stdin/stdout if not specified) and doesn't
support tty, pipes, etc.

The image format must be specified with -O for the output if the raw format
is not the intended one.

Two tests are added to test qemu-img dd.

Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
Message-id: 20160810024312.14544-1-fullmanet@gmail.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
[mreitz: Moved test 158 to 170]
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/common.rc

@@ -234,10 +234,7 @@ _check_test_img()
         else
             $QEMU_IMG check "$@" -f $IMGFMT "$TEST_IMG" 2>&1
         fi
-    ) | _filter_testdir | \
-        sed -e '/allocated.*fragmented.*compressed clusters/d' \
-            -e 's/qemu-img: This image format does not support checks/No errors were found on the image./' \
-            -e '/Image end offset: [0-9]\+/d'
+    ) | _filter_testdir | _filter_qemu_img_check
 }
 
 _img_info()