Slashes in agent-id break GoCD agent status link

[greglook]

Currently agents are identified using their Aurora slash-separated path name, e.g. aws-dev/gocd/prod/test-agent-0. This seems to work fine with GoCD, except for the link to view the status page for an agent. The slashes are not URL-escaped, so GoCD takes you to the wrong place and returns a 404. We could transform these so that they use a different delimiter inside the plugin, ideally one that is URL-safe already like :.