sw test tool: Enable IPv6 flow label maskable

OF 1.3.4 spec (B.15.1 Changes) says:

    Make IPv6 flow label maskable (EXT-101).

This patch makes IPv6 flow label maskable, and adds a test file for IPv6 flow label with masks.

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
package: add python-ryu-doc

This patch adds python-ryu-doc package which contains the HTML
documentation generated from doc/.
Also updates the man pages in doc/source/man/.

Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
app_manager: prevent loading unnecessary RyuApps

don't load RyuApps which is just imported and not defined in the module.
for example, if we run the script "test.py" as shown below by

$ ryu run test.py

the past implementation loads and instantiates not only Test but also RyuApp
and DPSet. this patch fix this wrong behavior

test.py
===

from ryu.base.app_manager import RyuApp
from ryu.controller.dpset import DPSet

class Test(RyuApp):
    _CONTEXTS = {'dpset' : DPSet}

Signed-off-by: ISHIDA Wataru <ishida.wataru@lab.ntt.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>