better support for VirtualBox sessions

[Antoine Martin]

r4569 makes VirtualBox sessions usable but has a number of limitations.

• password mode is broken? rdesktop/xfreerdp aren't very helpful with the error message here. (ie: "ERROR: send: Broken pipe")

(also when loading a session from disk: verify that the password we have is the right one by re-encoding it rather than always assigning a new one?)

• when the session fails to start we end up calling early_failure which sets it as UNAVAILABLE but this gets reset when the session data is parsed again. Either leave it as unavailable or...?
• we should fire call_when_done when the server log shows the port is ready rather than polling it. ie:

  VRDE server is listening on port 3389.
  VRDE server is inactive.
  

• support cloning via the UI (since we already enable multi-attach)
• allow local user to resume via SDL? Pure client-side session handling will complicate things..

etc..

[Antoine Martin]

r4622 fixes password mode: was an undocumented password size limit...

[Antoine Martin]

As per #212: we should distinguish running sessions from stopped ones (by adding a new SessionStatus).
(the "start" option will either start a VM or connect to it - no way to tell)

[onlyjob]

It would be better if powered down VMs would appear as standalone menu and become 'sessions' only when started.

Thanks.

[Eric Blade]

+1 to this. The virtualbox support had me super confused for a few minutes, while i had to track back through the fog of a year ago, and figure out just what the heck those things it was showing were. (i don't use vbox much .. last time a bit over a year ago.. but the vbox interface thought my images were all still there) And having them listed as "sessions" when they aren't even running just feels weird.