With openstacksdk prior to version 0.19, module volume_info fails with:
TypeError: Value of unknown type: <class
'openstack.block_storage.v2.volume.Volume'> ...
The call to 'self.conn.block_storage.volumes()' returns an instance
of class 'openstack.block_storage.v2.volume.Volume'. This class
inherits from 'openstack.resource.Resource', which is a 'dict'
subclass since 0.19. For older sdk versions prior to 0.19 it was
not, hence we have to use the 'to_dict' function to convert each
'Volume' to 'dict' explicitly.
Ref.: 2f97394847
Task: 41571
Story: 2008136
Change-Id: I5b7adc399f19da08f02202af64a226c92bb9bf41
all_projects is not supported before openstacksdk 0.19,
use min_ver for using it.
Task: 40865
Story: 2008136
Change-Id: I0f02a47c11122c5b07ca650a830044bca56c3610
