Fix up some unicode vs. bytes issues in rbtools.api
Review Request #9535 - Created Jan. 25, 2018 and submitted
There are a handful of places that were using the wrong data type within
the API wrappers in RBTools. This worked fine in Python 2 because
they're freely convertable, but would crash or otherwise fail under
Python 3. This change fixes those up.
Ran unit tests under Python 2.7 and 3.6.