Enable "Change Machine" for all targets who enabled rwhod

[junhaoliao]

Is your feature request related to a problem? Please describe.
The current front end client doesn't display the "Change Machine" button even though the target may support "ruptime" and has the rwhod demon running.

Describe the solution you'd like
Detect the capability at session creation and show "Change Machine" button on such sessions, assuming the user has login access to other machines listed by "ruptime".

Describe alternatives you've considered
Instead of auto-detection, let the user configure the capability at session creation, by providing a checkbox or slider.

Additional context
N/A