dockercompose: Add ability to suppress automatic links in UI (#6270)

[kinland]

There was a suggestion in #6270 to suppress the "http://localhost:${port}" links that get added automatically when using docker_compose. I liked the idea, so I took a swing at implementing this.

[kinland]

I'm not sure why TestShutdownOnCancel is failing on CircleCI. Seems to work locally:

=== RUN   TestShutdownOnCancel
Running cmd: sh -c "function cleanup()\n{\n  echo \"cleanup time!\"\n  exit 1\n}\n\ntrap cleanup EXIT\nsleep 100"
About to gracefully shut down process 95745
--- PASS: TestShutdownOnCancel (1.01s)