Allow manila share to be referenced by name

Currently, in order to reference a manila share, you must include the share-id. This proposed change allows for a manila share to be referenced by its name in addition to the id to facilitate easier use by the end user. It will also be more in-line with the current openstack convention of referencing an object by name or by id.

Given that this is a fairly straightforward and small feature, no spec will be written.