osprofiler @trace decorator fails with unicode

[Paul Karikh]

@trace decorator fails on this line: https://github.com/openstack/osprofiler/blob/master/osprofiler/profiler.py#L150
when function args have unicode in their argument.
In my case it was the following dict:
{"name": u'\u4e91\u89c4\u5219',
 "status": "ACTIVE",
 "tenant_id": tenant3.id,
 "server_id": "3"}
Full dataset is here: https://github.com/openstack/horizon/blob/master/openstack_dashboard/test/test_data/nova_data.py#L454
Without @profiler.trace() Horizon tests work fine so looks like there could be an issue in decorator.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Tovin Seven (<email address hidden>) on branch: master
Review: https://review.openstack.org/448883