added some fault handling

Signed-off-by: James Paton <jpaton2@gmail.com>
Merge branch 'master' of github.com:igorcanadi/FreEBS
use work_queue for sending; (more) gracefully fail without putting things into D state

Signed-off-by: James Paton <jpaton2@gmail.com>
Merge branch 'master' of github.com:igorcanadi/FreEBS