'Convert the volume to be of the new type.
Returns a boolean indicating whether the retype occurred.
:param ctxt: Context
:param volume: A dictionary describing the volume to migrate
:param new_type: A dictionary describing the volume type to convert to
:param diff: A dictionary with the difference between the two types
:param host: A dictionary describing the host to migrate to, where
host[\'host\'] is its name, and host[\'capabilities\'] is a
dictionary of its reported capabilities (Not Used).'

@datc._api_lookup
def retype(self, ctxt, volume, new_type, diff, host):

    pass
