qemu testcase "qemu_img.info" runs failed

[lijuanmen]

The content of the config file is as followed:

include tests-shared.cfg

variants:
- @qemu_kvm_jeos_quick:
only (image_backend=filesystem)
only no_9p_export
only no_pci_assignable
no hugepages
no multi_host
only RHEL.7.0
qemu_binary = /usr/libexec/qemu-kvm
qemu_img_binary = /usr/bin/qemu-img
qemu_io_binary = /usr/bin/qemu-io
only qcow2
only virtio_net
only virtio_blk
only smp2
no q35
only io-github-autotest-qemu.qemu_img.info

When running virttest ,the result was always failed. Because in the script, the variation of image size is always 10G ,and it will not change with the actual image size.