53af0dd72f
We should warn users who use the `--dns` command line option to point DNS to a localhost address, either IPv4 or IPv6. Unless they have specifically set up the container as a DNS server or are using --net=host (which is why this should be allowed, but warned on because those are pretty unique cases) a localhost address as a resolver will not reach what they might expect (e.g. expecting it will hit localhost on the Docker daemon/host). Added a test for the message, and fixed up tests to separate stdout and stderr that were using `--dns=127.0.0.1` to test the options. Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp) Upstream-commit: afa92a9af0f1a77ef25aab73b11aa855a1823666 Component: engine