Bugfix: AttributeError: 'dict' object has no attribute 'encode'

Bugfix: AttributeError: 'dict' object has no attribute 'encode'

JIRA: YARDSTICK-557

If we run task with sample/ping.yaml
We will encounter below error, here is the log:
Traceback (most recent call last):
File "/usr/local/bin/yardstick", line 11, in <module>
load_entry_point('yardstick==0.1.dev0', 'console_scripts',
        'yardstick')()
File "/usr/local/lib/python2.7/dist-packages/yardstick/main.py",
line 49, in main
YardstickCLI().main(sys.argv[1:])
File "/usr/local/lib/python2.7/dist-packages/yardstick/cmd/cli.py",
line 167, in main
self._dispath_func_notask()
File "/usr/local/lib/python2.7/dist-packages/yardstick/cmd/cli.py",
line 145, in _dispath_func_notask
func(CONF.category)
File
"/usr/local/lib/python2.7/dist-packages/yardstick/cmd/commands/task.py",
line 45, in do_start
Task().start(param, **kwargs)
File
"/usr/local/lib/python2.7/dist-packages/yardstick/benchmark/core/task.py",
line 83, in start
self._run(scenarios, run_in_parallel, args.output_file)
File
"/usr/local/lib/python2.7/dist-packages/yardstick/benchmark/core/task.py",
line 131, in _run
runner = run_one_scenario(scenario, output_file)
File
"/usr/local/lib/python2.7/dist-packages/yardstick/benchmark/core/task.py",
line 410, in run_one_scenario
if is_ip_addr(scenario_cfg["target"]):
    File
    "/usr/local/lib/python2.7/dist-packages/yardstick/benchmark/core/task.py",
    line 358, in is_ip_addr
    ipaddress.ip_address(addr.encode('utf-8'))
    AttributeError: 'dict' object has no attribute 'encode'

Change-Id: Iba1570416bd8614e38c9e847de730a31d9ddedc2
Signed-off-by: chenjiankun <chenjiankun1@huawei.com>