qemu-io: Add failure regression tests

Add regression tests checking that qemu-io fails with non-zero exit code
when reading non-existing file or using the wrong image format.

Signed-off-by: Nir Soffer <nirsof@gmail.com>
Message-id: 20170201003120.23378-4-nirsof@gmail.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
