[CLI] Automatically attach CLIs if corresponding Runtime process is active

[levincent06]

For all the CLIs, they spawn an instance of Runtime if not using the attach argument. It's disastrous if we accidently run CLIs without attach when Runtime is already running. For each CLI (and shm_ui), if Runtime is already running we should print a warning and perform the same behavior as if the attach argument had been set.

This may be one way to do it: https://www.unix.com/programming/146092-how-do-i-check-if-process-running-c.html