jsonalchemy: fix problem with reserved names

* Addresses issue when `try_to_eval` function was evaluating missing
  subfields to existing global Python functions.  (closes #2593)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
@lnielsen-cern this should allow using any string except ones from `__builtins__` functions.

@jalavik If you want `"type"` to be evaluated as string use `"str(type)"`.