This adds the capability to turn on user namespace support when using an
experimental build Docker daemon binary using the `--userns-remap` flag.
Also documentation is added to the experimental docs.
Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)
Upstream-commit: 44e1023a93a0107d63d5400695cbbc6da498a425
Component: engine