sw test tool: Enable sending packets using random values

The switch test tool is now enabled to send packets using random values as follows:

        "tests":[
            {
                "ingress":{
                    "packets":{
                        "data":[
                            "ethernet(dst=netaddr.EUI(randint(0, 2 ** 48 - 1)), ethertype=2048)",
                            "ipv4(proto=6, src=netaddr.IPAddress(randint(0, 2 ** 32 - 1)))",
                            "tcp(dst_port=http://goo.gl/2gWwFs)",
                            "str(\"\\x11\" * (1500 - 54))"
                        ],
                        "pktps":1000,
                        "duration_time":30
                    }
                },
                "egress":[
                    "ethernet(ethertype=2048)",
                    "ipv4(proto=6)",
                    "tcp()",
                    "str(\"\\x11\" * (1500 - 54))"
                ]
            }
        ]

When ingress.packets.data includes 'randint', the switch test tool will send each packet using random values.

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Optimize similar methods

 - _test_flow_install()
 - _test_meter_install()
 - _test_group_install()

are merged as

 - _test_msg_install()

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Remove unused codes

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: pylint

W:573,14: Access to a protected member _send_msg of a client class (protected-access)

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Add default test files (group)

These test files aim to examine 'group action' of FlowMod message.

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>