Update to use latest function_trace

latest function_trace contains non-backward compatible changes. I tried not to introduce changes to the interface but at least they are straightforward.  See https://github.com/RedHatQE/function_trace/commit/32e8dc640b5038af7f9c2fd00bc2a4d513f5523e

This PR updates to call `function_trace.trace_on` in the new way, and removes the PIP version restriction to once again allow the latest version.

Also contains a fix for a bug in a `getattr` method that was exposed by the latest function_trace.