scenario tests use the following environment.

diagram:

       ----------------------+--------------- tenant
                             |                network
                        +--------+
                        | router |
                        +--------+
                             |
       -----+----------------+--------------- provider
            |                |                network
       +---------+           |
       | dragent |           |
       +---------+           |
            |                |
            | +--------------+
            | |
       +--------+
       | docker |
       | bridge |
       +--------+
            |
            +-----------+------------+-------
                        |            |
                   +---------+  +---------+
       docker      | quagga1 |  | quagga2 | ...
       container   +---------+  +---------+


docker container environment is provided by test tool of ryu.
It has the following functions:
- build and remove a container image.
- run, stop and remove a container.
- some operations to quagga container.
- get some information from quagga container.
