qemu-img: improve error reporting

Use strerror to provide a better error message when qemu-img fails.

https://bugs.edge.launchpad.net/ubuntu/+source/qemu-kvm/+bug/418112

Signed-off-by: Dustin Kirkland <kirkland@canonical.com>

diff -uprN qemu-kvm-0.11.0~rc2/qemu-img.c qemu-kvm-0.11.0~rc2.new/qemu-img.c
--- qemu-kvm-0.11.0~rc2/qemu-img.c	2009-08-30 04:10:59.000000000 -0500
+++ qemu-kvm-0.11.0~rc2.new/qemu-img.c	2009-09-10 22:30:32.572211443 -0500
@@ -368,7 +368,7 @@ static int img_create(int argc, char **a
         } else if (ret == -EFBIG) {
             error("The image size is too large for file format '%s'", fmt);
         } else {
-            error("Error while formatting");
+            error("Error while formatting (%s)", strerror(-ret));
         }
     }
     return 0;