Could we grab all these things from a stackrc file, and just specify e.g. --stackrc-path as a single argument?

This would allow the uses of this plugin to become more concise, e.g.:
`sensu_check: name=check-nova-api plugin=check-os-api.rb args='--stackrc-path /root/stackrc --port 9292 --path /v1/images --match-str images'`

More importantly, having these creds in the command line options means that these admin creds will be sent to pagerduty, through unencrypted email, etc.