get last commit id for pipeline in pps watch api server implementation
get last commit id for pipeline in pps watch api server implementation

ShengjieLuo/pachyderm,klucar/pachyderm,sambooo/pachyderm,ShengjieLuo/pachyderm,alexdebrie/pachyderm,alexdebrie/pachyderm,klucar/pachyderm,klucar/pachyderm,sambooo/pachyderm,sambooo/pachyderm,alexdebrie/pachyderm,ShengjieLuo/pachyderm