Support parameterization of hard-coded SIMS attributes

Certain node attributes are hard-coded into test_utils.py and test_utils_rfc8040.py, including username (openroadm), password (openroadm), and host (127.0.0.1). To facilitate using the existing tox testing framework for physical devices, we propose to add support for username, password, and host as additional optional key-value pairs in the simulators.py file.

If the new key-value pairs are not present in simulators.py, the normal defaults will apply. In order to take advantage of this new feature, the person doing the testing of physical devices would need to edit the simulators.py file by hand.

E.g.:

SIMS = {    ('xpdra', '1.2.1'): {'port': '17830', 'configfile': 'oper-XPDRA.xml', 'logfile': 'xpdra-121.log', 'username': 'person123', 'password': 'MyPassword', 'host': '192.168.5.55'},

Additionally, if the start_sims function sees that a particular node has a host override specified in the SIM dictionary, it will skip starting a Honeynode instance for it. This would potentially allow for mixed physical/honeynode test environments.