Add capabilities for gdb to work

[Jack Hale]

Currently the Docker container is heavily sandboxed and gdb won't run.

'Runtime privilege and Linux capabilities'

https://docs.docker.com/engine/reference/run/

Do enough --cap-add to get it working.

[Jack Hale]

#!
--security-opt=seccomp=unconfined --cap-add=SYS_PTRACE

First option less than ideal security wise but I guess people aren't running the debug version in the cloud.

[Jack Hale]

Added automatically when user asks for new dev-env-dbg based image.