Fixes#1636
New format now generates a UUID and includes it along with
the order of disks. So that UUID is the real order of disks
and on command line user is able to specify disks in any order.
This pre-dominantly solves our dilemma.
```
{
"format" : "xl",
"xl" : {
"version" : "1",
"disk": "00e4cf06-5bf5-4bb5-b885-4b2fff4a7959",
"jbod" : [
"00e4cf06-5bf5-4bb5-b885-4b2fff4a7959",
....
"c47d2608-5067-4ed7-b1e4-fb81bdbb549f",
"a543293e-99f1-4310-b540-1e450878e844",
"18f97cbe-529a-456a-b6d4-0feacf64534d"
]
},
"version" : "1"
}
```
