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
