USB controllers can share the same 'index' which indicates, that there
is some sort of master-companion relationship.  Reorder the controllers
in XML in to place the master controller before its companions.  This is
required by QEMU to not fail with error message:

error: internal error: process exited while connecting to monitor:
2015-10-26T16:25:17.630265Z qemu-system-x86_64:
-device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x6:
USB bus 'usb.0' not found

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1166452Signed-off-by: NPavel Hrdina <phrdina@redhat.com>