OrderedDict should be transformed in user-friedly form in `task detailed`

[Andriy Kurilin]

Value of "args values" in `rally task detailed` looks unreadable for users. Example http://paste.openstack.org/show/195309/

One of possible fixes: use "json.dumps"

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/167187

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/167187
Committed: https://git.openstack.org/cgit/stackforge/rally/commit/?id=a7635a1a3fada2e199f4876d07e0e405dce64ffc
Submitter: Jenkins
Branch: master

commit a7635a1a3fada2e199f4876d07e0e405dce64ffc
Author: Kun Huang <email address hidden>
Date: Tue Mar 24 22:43:19 2015 +0800

    Fix rally task start output format

    The old output:
        args values:
        OrderedDict([(u'runner', OrderedDict([(u'type', u'constant')...

    This patch makes output like:
         args values:
         {
           "runner": {
             "type": "constant",
             "concurrency": 10,
             "times": 100
           },
           "args": {
             "name_length": 10
           }
         }
    Change-Id: Ifbc3c110994974321bcccd767f836aaa6d02ef07
    Closes-Bug: #1435294