debian: Also insert authd as NSS source on reinstall (#461)

debian: Also insert authd as NSS source on reinstall

The debian/postrm script removes authd as a source from
/etc/nsswitch.conf, but the debian/postinst script only added it when
the package was installed for the fist time. That led to NSS not using
authd as a source when the package was reinstalled.

We now ensure that authd is always added as a source to the `passwd`,
`group` and `shadow` databases in /etc/nsswitch.conf when the authd
package is installed.

That's done by always calling `insert_nss_entry` on install, which is
already implemented so that it only adds the `authd` string to those
`passwd|group|shadow` lines in /etc/nsswitch.conf which don't already
contain it, so we can just always call that function on install.

UDENG-3906

debian/postinst

@@ -32,11 +32,5 @@ action="$1"
 
 if [ configure = "$action" ]; then
     pam-auth-update --package
-
-    if [ -z "$2" ]; then
-        log "First installation detected..."
-        # first install: setup the recommended configuration (unless
-        # nsswitch.conf already contains authd entries)
-        insert_nss_entry
-    fi
+    insert_nss_entry
 fi