Fix an issue where you couldn't run 'all' command inside container

[withinboredom]

• What I did
  Ignores itself instead of trying to stop itself if running from inside a docker container
• How I did it
  Check to see if there's a /proc/1/cgroup folder/file and if so, use that as an id to exclude
• Does it need a test written for it?
  Maybe??
• Description for the changelog
  Don't try to stop the container it may be running in
• Does it pass a ShellCheck? (excluding changes to .bats files see our CONTRIBUTING.md)
  Yes

[withinboredom]

This might open the door for an exclusion flag as well ... which would be nice (don't stop containers with name=something or something like that.

Let me know if I can make this better!

[withinboredom]

PS: this should be compatible with docker 1.8 +

[killianbrackey]

Thanks again! We plan on writing some more tests and refactoring a bit so we will keep you in the loop!

[kilpatty]

Thanks for all the pulls! We really appreciate the great work!

[withinboredom]

Welcome, glad I could be of service -- your project just became part of dev environment and build maintenance scripts (this project is way more thorough than spotify/docker-gc)!