Modify generate_methods to take vargs

This patch modies generate_methods to take vargs instead of the
sequence. Previously you needed to call it as follows:

    @generate_methods([LIST, SHOW, CREATE, UPDATE, DELETE])

But with this patch you can call it like below:

    @generate_methods(LIST, SHOW, CREATE, UPDATE, DELETE)

Signed-off-by: Taku Fukushima <tfukushima@midokura.com>