bump(net-misc/gsutil): Bump gsutil to version 3.31, add dependencies

This includes a new gsutil verison which is not yet in upstream portage
along with new ebuilds for a couple of its dependencies that are also
not in portage:
    dev-python/google-api-python-client
    dev-python/socksipy-branch

Also, dev-python/python-gflags is included here to apply two extra
patches that fix some unit tests and add mark that it conflicts with the
old version of dev-cpp/gflags that we had been using up until now.

Hopefully all this will be merged upstream soon:
    https://bugs.gentoo.org/show_bug.cgi?id=468080