Improve UX when there is a broken terminal emulator

[ethanpailes]

Right now the program to be debugged will just spin silently if the terminal emulator we have chosen to launch fails. It would be a better user experience if the program to be debugged just slept for a second before complaining that the terminal emulator failed to launch. I can't think of a way to do this that is compatible with the old debug-here-gdb-wrapper, so we might need to cut a new version of that, which is a little unfortunate.