services/base: make get_method get all params if param_names is None
services/base: make get_method get all params if param_names is None

The further optimizes the common case of grabbing all parameters of a
method (while skipping over 'self').

ducksboard/libsaas,livingbio/libsaas,CptLemming/libsaas,80vs90/libsaas