rfe: permit device owner login to device / dev mode

[msherman64]

As seen in #38
there's a valid use case for device owners to ssh to, and directly manage their devices.

Actually making this useful requires further design, to ensure the device supports ssh login, has keys added, and that the security model still makes sense.

We have provided a web dashboard for this mechanism in FLOTO, but lack something similar for CHI@Edge.