Wrong hint key in volume create function

Hint key has to be 'OS-SCH-HNT:scheduler_hints' not 'scheduler_hints'
and scheduler_hints key has to be located in same level with volume.

Change-Id: Ic5888545d4b7ee6bb58a22840928ef1fc86fedfa
Closes-Bug: #1276088
Merge "Wrong hint key in volume create function"