Fixed disk claim and release for sw raid

(cherry picked from commit 02ef87b4752690cf322ba7cf25550358b2972f27)
Extended ohai block_device for unique names

(cherry picked from commit 9c79052e4c535583aed36f2a686ed2f0fdc86b96)
Merge pull request #195 from vuntz/swraid-roxy

Backport of software raid to roxy