sw test tool: Remove an unnecessary wrapper method

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

TargetSw and TesterSw are merged as OpenFlowSw.

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

OpenFlowSw.del_test_flow() and OpenFlowSw.del_flows_for_throughput_analysis() are merged as OpenFlowSw.del_flows().

And rename OpenFlowSw.del_test_meter() to OpenFlowSw.del_meters(), like OpenFlowSw.del_flows().

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

_test_initialize_flow_tester() is merged into _test_initialize_flow().

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

All of xxx_stats_reply_handler() are merged as stats_reply_handler().

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Reduce similar methods of checking entries exist

All of _test_xxx_exist_chk() are merged as _test_exist_chk().

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Improve difference analysis of packets

Using difflib instead of an original method.

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

E:1026, 8: Instance of 'DummyDatapath' has no 'set_xid' member (but some types could not be inferred) (maybe-no-member)
E:1027, 8: Instance of 'DummyDatapath' has no 'send_msg' member (but some types could not be inferred) (maybe-no-member)

NOTE: These methods are never called. This patch is only for avoiding pylint error.

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