Merge pull request #637 from xutian/block_copy_fix

Bug fix in block_copy tests
qemu.tests: disable qemu_iotests for some image format on RHEL host

since qcow, qed, vmdk, vpc and vdi not support by qemu-kvm in RHEL so
filter out tests on these image format;

Signed-off-by: Xu Tian <xutian@redhat.com>