Work around uWSGI collecting wsgi_environ.iteritems() during iteration
Work around uWSGI collecting wsgi_environ.iteritems() during iteration

If iteritems() is accessed after being collected, the refcount is zero and we get this error:
```
../Objects/tupleobject.c:142: bad argument to internal function
```
Therefore, take a copy so uWSGI can't take the carpet out from under us.

uber-common/opentracing-python-instrumentation,uber-common/opentracing-python-instrumentation