qemu: Assume QEMU_CAPS_DISK_SHARE_RW

qemu: Assume QEMU_CAPS_DISK_SHARE_RW

Introduced in QEMU's commit of v2.9.0-rc0~48^2~25 the .share-rw
attribute of virtio-blk device is always available for all QEMU
versions we support (4.2.0, currently). Therefore, we can assume
the capability is always set and thus doesn't need to be checked
for.

The change in controller-order.args is justified, because the
qemuxml2argvdatatest runs the test case with very minimalistic
set of capabilities, that's nowhere near real life scenario.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>