Fix #35 (verilator getting stuck) and add ci test

[andreaskuster]

This PR should fix #35. In addition, we should add a test case to the CI to ensure that verilator support persists. Right now, I set the environment variable SIM=verilator, however, we should test icarus and verilator before we merge this.

[alexforencich]

Thanks for the PR, but I'm not interested in making any changes here to support verilator until verilator/verilator#2778 is fixed and cocotb works with the latest release version of verilator.

[andreaskuster]

Fair enough. Let´s keep this open, since I still think there is the buggy verilator issue you mentioned, however there is a good chance that something broke in cocotb-bus > 0.1.1

[benreynwar]

Just hit this same issue trying to run test_axi_interconnect.py using a new version of verilator (with the above mentioned bug fixed)
Verilator 5.007 devel rev v5.006-7-g4a8cfe367

Switching to using cocotb-bus==0.1.1 fixed the issue for me.

[alexforencich]

Upstream verilator issue is verilator/verilator#3919