block-job-complete : retry if block job cannot be complete

Even if we check the busy flag, we can have sometime race condition if new write
are coming between the query-block-job and the block-job-complete.

block-job-complete throw an error "The active block job for device '%(name)' cannot be completed"

we just need to retry in this case.

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
delete trailing whitespace
bump version to 3.3-3