Add Automated Tests For Crossbar Routers Connected With RLink

[Skully17]

In response to the comment made here: #2079 (comment), I have written some automated that tests any scenarios that came to mind and, most importantly, re-creates the errors that I fixed in this PR: #2080.

The code can be found here: https://github.com/Skully17/playground/blob/master/crossbar_tests/test_rlink.py
Please let me know if there is another way you would like me to share the code.

I have not made a PR for two reasons:

1. I don't know where it would be suitable to put these tests in the Crossbar project
2. I assume that there are some changes that will need to be made before it is satisfactory

During the making of these tests I found another issue that I fixed and a potential issue that needs more investigation.