Containers crash if 'crossbar' is configured in site-config file

[BrianJKoopman]

If there is a 'crossbar' configuration under any host in the ocs site config file, and that config file is used to startup Agents within Docker containers, those Agents will fail during site_config setup.

Example in site-config file:

  any-hostname: {
  'crossbar': {'config-dir': './dot_crossbar/'},
    'agent-instances': []
  }

Resulting crash:

2021-09-01T20:53:44+0000 Traceback (most recent call last):
2021-09-01T20:53:44+0000   File "aggregator_agent.py", line 156, in <module>
2021-09-01T20:53:44+0000     args = site_config.parse_args(agent_class='AggregatorAgent',
2021-09-01T20:53:44+0000   File "/app/ocs/ocs/site_config.py", line 700, in parse_args
2021-09-01T20:53:44+0000     site, host, instance = get_config(pre_args, agent_class=agent_class)
2021-09-01T20:53:44+0000   File "/app/ocs/ocs/site_config.py", line 424, in get_config
2021-09-01T20:53:44+0000     site_config = SiteConfig.from_yaml(site_file)
2021-09-01T20:53:44+0000   File "/app/ocs/ocs/site_config.py", line 62, in from_yaml
2021-09-01T20:53:44+0000     self = cls.from_dict(data)
2021-09-01T20:53:44+0000   File "/app/ocs/ocs/site_config.py", line 53, in from_dict
2021-09-01T20:53:44+0000     self.hosts[k] = HostConfig.from_dict(v, parent=self, name=k)
2021-09-01T20:53:44+0000   File "/app/ocs/ocs/site_config.py", line 110, in from_dict
2021-09-01T20:53:44+0000     self.crossbar = CrossbarConfig.from_dict(data.get('crossbar'))
2021-09-01T20:53:44+0000   File "/app/ocs/ocs/site_config.py", line 139, in from_dict
2021-09-01T20:53:44+0000     raise RuntimeError("Unable to locate crossbar binary")
2021-09-01T20:53:44+0000 RuntimeError: Unable to locate crossbar binary

[BrianJKoopman]

Fixed in #241.