'Loads the credentials from their source & sets them on the object.
Subclasses should implement this method (by reading from disk, the
environment, the network or wherever), returning ``True`` if they were
found & loaded.
If not found, this method should return ``False``, indictating that the
``CredentialResolver`` should fall back to the next available method.
The default implementation does nothing, assuming the user has set the
``access_key/secret_key/token`` themselves.
:returns: Whether credentials were found & set
:rtype: boolean'

def load(self):

    return True
