kojivmd: pass "-F qcow2" to qemu-img create
    
    In RHEL 9 (qemu-img-6.2.0-11.el9_0.3), the "qemu-img create" command
    requires the "-F" flag that specifies the second image's format.
    
    qemu-img-1.5.3-175.el7_9.6 recognizes this -F flag also, so it should be
    safe to use on all supported platforms.