useradd-staticids: don't create username-group if gid is specified

Adding distcc to an image, and having staticids enabled,
doesn't work as it causes a a superfluous 'distcc' group
being added using a conflicting  GID, thus failing the
build:
 | ERROR: distcc-3.2-r0 do_prepare_recipe_sysroot: distcc: groupadd command did not succeed.

Compared to other recipes, the distcc recipe only
specifies --gid for the primary group, and doesn't specify
--no-user-group, but when --gid is given, it doesn't make
sense to create a matching username-group in addition,
even if --no-user-group was not specified, and 'useradd'
actually complains if --gid and --user-group are given
both.

If only --gid is given, the current code in here
effectively behaves as if --user-group was specified,
taking the group-id of the username-group from the
--gid parameter. This causes the error above, as we try
to add a new group (distcc) with an existing group-id
(nogroup).

This is contrary to the comment in this file just above,
contrary to what useradd can do, contrary to behaviour
without the useradd-staticids bbclass, and non-intuitive.

Change the code such that a username-group is only created
- if a primary group using --gid was not specified, or
- if --no-user-group was not specified

To be in line with useradd, if gid is not given, and
--no-user-group is given, we add the user to the group
'users', which mimics useradd's behaviour.

(From OE-Core rev: b1843e60ebe534243b49f3685540fa5ea49d5f35)

Signed-off-by: André Draszik <adraszik@tycoint.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

(cherry picked from commit fc3a86ae68919cec72c1a8ae0f9ba1f98ae13f0d)
Signed-off-by: André Draszik <adraszik@tycoint.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/useradd-staticids.bbclass

@@ -141,9 +141,13 @@ def update_useradd_static_config(d):
             # So if the implicit username-group creation is on, then the implicit groupname (LOGIN)
             # is used, and we disable the user_group option.
             #
-            user_group = uaargs.user_group is None or uaargs.user_group is True
-            uaargs.groupname = uaargs.LOGIN if user_group else uaargs.gid
-            uaargs.groupid = field[3] or uaargs.gid or uaargs.groupname
+            if uaargs.gid:
+                uaargs.groupname = uaargs.gid
+            elif uaargs.user_group is not False:
+                uaargs.groupname = uaargs.LOGIN
+            else:
+                uaargs.groupname = 'users'
+            uaargs.groupid = field[3] or uaargs.groupname
 
             if uaargs.groupid and uaargs.gid != uaargs.groupid:
                 newgroup = None