Fix iotest 153

Commit f62514b3def5fb2acbef64d0e053c0c31fa45aff made qemu-img reject -o "" but this test uses it.
Since this test only tries to do a dry-run run of qemu-img amend,
replace the -o "" with dummy -o "size=$size".

Fixes: f62514b3def5fb2acbef64d0e053c0c31fa45aff

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20200504131959.9533-1-mlevitsk@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
2 files changed