API error when throwing a merge conflict error

[pholleran]

See #33 for the full error stack

When a merge conflict is detected an error is thrown by the report_error method. This method calls client.create_issue, referencing the client object created here which uses the originating token, but does not take in to account that it may be an Enterprise repository (which it is in this case).

I think a better approach would be to create two different clients: origin_client and destination_client, referencing them each at the proper place in the code. This will make explicit the intended destination of each API call and handle them appropriately.