Fix config loading when running the Tuskar API

This regression was caused in d0a5513e7f539501923cca73f3dc63522dfad7a5
as the rpc service integration code has a side effect of loading the
configuration file.

Unfortunately this issue wasn't picked up during that initial cleanup as
the API entrypoint doesn't have test coverage.

Change-Id: I50cef8855828ca51957572ddf48a4761859876b4
Closes-bug: #1357525
Merge "Fix config loading when running the Tuskar API"