UI: Update acceptance tests to use PageObjects

Fix reload issue for TLS certificates in dev mode

Fix and speedup rkt tests

scheduler: fixed nil panic and clearer error handling

UI: Refactor breadcrumbs

UI: Codify common mirage scenarios and make it easy to switch between

Disable networking when it's not needed and improve failure message for
UserGroup test by including the full ps output on failure.

Even when net=none we would attempt to retrieve network information from
rkt which would spew useless log lines such as:

```
testlog.go:30: 20:37:31.409209 [DEBUG] driver.rkt: failed getting network info for pod UUID 8303cfe6-0c10-4288-84f5-cb79ad6dbf1c attempt 2: no networks found. Sleeping for 970ms
```

It would also delay tests for ~60s during the network information retry
period.

So skip this when net=none. It's unlikely anyone actually uses net=none
outside of tests, so I doubt anyone will notice this change.

Official docs:
https://coreos.com/rkt/docs/latest/networking/overview.html#no-loopback-only-networking