Add basic volume management methods for Linode: destroy_volume(), ex_create_volume(), ex_list_volumes().
The Linode node comes with persistent storage which can be divided to volumes. This pool of storage can't be disconnected from the particular Linode or connected to other one. So for every operation on volumes one have to provide specific LinodeID. This is the reason why ex_ methods have been created.
In order to destroy volume one have to provide StorageVolume instance as a parameter to destroy_volume(). Because this method checks StorageVolume.extra["LINODEID"] for LinodeID it can be standard libcloud API method. By default ex_list_volumes() returns volume instances with extra["LINODE"]