When processing the --userns-remap flag, add the capability to call out to `getent` if the user and group information is not found via local file parsing code already in libcontainer/user. Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> Upstream-commit: 6cb8392be9cdc5bf44436a092dd88b39968ffc7d Component: engine