nss-localuser: Add the NSS plugin for localuser

nss-localuser: Add the NSS plugin for localuser

`nss-localuser` is a plugin for the GNU Name Service Switch (NSS)
functionality of the GNU C Library (`glibc`) providing host name
resolution for *"localuser"* family of virtual hostnames.

The delivered NSS service defines one virtual host of name `localuser`
that resolves to an IP address of the localhost loopback that integrates
user ID.

Bug-AGL: SPEC-1833

Change-Id: I8ce87297a220e8c691cdbea00262d873b68ffd75
Signed-off-by: José Bollo <jose.bollo@iot.bzh>