makedevs: support using user/group names in device table files

makedevs: support using user/group names in device table files

Compared to hard coding the numeric group and user ids in the device
table files, the way of using user/group names is preferred.

This patch adds the ability to makedevs to correctly deal with device
table files with user/group names in them.

To maintain backward compatibility, the way of using uid/gid is still
supported.

[YOCTO #1159]

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>