We make the check more user-friendly, and users can learn start docker with wrong fd used. Signed-off-by: Kai Qiang Wu(Kennan) <wkqwu@cn.ibm.com> Upstream-commit: 3c69d340ebe35dc3adb56cd2345cbac3c1dd5fb8 Component: engine
docker.go contains Docker's main function.
This file provides first line CLI argument parsing and environment variable setting.