ui/ncurses: Spin child to ensure autoboot cancelled on exit

ui/ncurses: Spin child to ensure autoboot cancelled on exit

If the client is not connected to the server instance when exiting, fork
and have the child process spin until the server is available and can be
told to cancel autoboot. This prevents the scenario of a user exiting
the UI and having the server continue to autoboot while they are using
the command line.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
(cherry picked from commit 1dd51e986202e5e111c1042f148867bd08c2bedc)