virsh_domxml_to_native test improvements

Various changes to make the test function:
    Adjust the read process cmdline based on the knowledge that on
        Fedora 18 or later host, the qemu-kvm command line argument
        can be changed to be "qemu-system-x86_64 accel=kvm"
    Adjust the splitting of the command line from a list of each element
        that was separated by a space to a more ordered and natural
        looking list of items with "-option [arg]" on one line rather
        than adjacent "-option" "argument" elements
    Adjust the logic to perform better diffs using sets and determining
        what is in one list and not the other
    If differences are found, print them and in which order to make for
        easier debugging of problems

Signed-off-by: John Ferlan <jferlan@redhat.com>
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Merge pull request #898 from Antique/virsh_domxml_to_native

virsh_domxml_to_native test improvements