plugin : has_feature : clone from base + fix

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
rbd : has_feature : clone from base

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
sheepdog : has_feature : clone base

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
nexenta : has_feature : clone base

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
bump version to 2.3-3