In order to avoid unfortunate collisions with statically assigned
container account UIDs and GIDs, cap normal users at 9999. That way
we can set our containers to use IDs 10000 and above.
Make sure adduser/addgroup's adduser.conf gets adjusted to match the
values we set in the login.defs referenced by the lower-level
useradd/groupadd tools too. We're not using non-Debian-derivative
servers these days, so don't bother to try making this work on other
distributions for the time being.
Change-Id: I0068d5cea66e898c35b661cd559437dc4049e8f4
698bb3df21