get_auth_info in chaosreliably.__init__.py tries to reference a non-existent key

[ciaransweet]

When an experiment with a top level entry of:

"secrets": {
  "reliably": {
    "host": "a-host"
  }
}

And action entry of:

"provider": {
    "type": "python",
    "module": "chaosreliably.slo.probes",
    "func": "get_last_N_slos",
    "arguments": {
        "quantity": 1
    },
    "secrets": ["reliably"]
},

Is provided, the get_auth_info function mistakenly tries to do:

reliably_secrets = secrets.get("reliably", {})

This always results in reliably_secrets={} because secrets={"host": "a-host"}.

The block here https://github.com/chaostoolkit-incubator/chaostoolkit-reliably/blob/master/chaosreliably/__init__.py#L81-L83 should instead be:

secrets = secrets or {}
reliably_token = secrets.get("token")
reliably_host = secrets.get("host")