fix usage of need_default in parse_storage_policies

The need_default varible in parse_storage_policies seems to mark the
case that there no policy is set to default. If True, the function trys
to use first policy as default. If False, that means there is a policy
is set yes for default option, not false values. So set need_default
False only if a policy says he is the default one.

Change-Id: Idc293366e6c529423e75900783570ffb6925533b
Merge "fix usage of need_default in parse_storage_policies" into feature/ec