xenlight: sort the VIFs into VIF.device order before we attach them to a new VM
xenlight: sort the VIFs into VIF.device order before we attach them to a new VM

Linux frontends enumerate VIFs in the order they're found in 'xenstore-ls'.
The order of 'xenstore-ls' is determined by the order of 'xenstore-write'.
The order of 'xenstore-write' is determined by the order of 'nics' passed
to the libxl domain_create call.

Fixes #31

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

djs55/xenopsd-previous,cheng--zhang/xenopsd,simonjbeaumont/xenopsd,johnelse/xenopsd,thomassa/xenopsd,djs55/xenopsd-previous,djs55/xenopsd-previous,djs55/xenopsd,koushikcgit/xenopsd,euanh/xenopsd,cheng--zhang/xenopsd,thomassa/xenopsd,simonjbeaumont/xenopsd,thomassa/xenopsd,johnelse/xenopsd,euanh/xenopsd,koushikcgit/xenopsd,djs55/xenopsd,simonjbeaumont/xenopsd,cheng--zhang/xenopsd,djs55/xenopsd,koushikcgit/xenopsd,euanh/xenopsd,johnelse/xenopsd