Add underscore support to generate_methods

This patch modifies generate_methods decorator to count
underscores as the lagitimate alias name.

Change-Id: I25c0b0bf4794213cf9e4702e121cbeaae630eb08
Signed-off-by: Taku Fukushima <tfukushima@midokura.com>
Merge "Add underscore support to generate_methods"