useradd.bbclass: Fix order of postinst-useradd-*

useradd.bbclass: Fix order of postinst-useradd-*

postinst-useradd-* haven't been running in order of dependency.

This patch is reworked from Piotr Łobacz's patch and fixes:

https://bugzilla.yoctoproject.org/show_bug.cgi?id=15084
https://bugzilla.yoctoproject.org/show_bug.cgi?id=13904

basepasswd_sysroot_postinst in base-passwd can install postinst-useradd-*
scripts with any order. Sometimes this means, for example a useradd postinst
will attempt to run without the corresponding group postinst causing errors.
This patch ensures that we first run groupadd, then useradd and then
group membership.

[RP: Tweaked to avoid removing previous fixes and for whitespace/style issues
     Also ensure the scripts are changed to execute with -e to highlight errors]

Signed-off-by: Eilís 'pidge' Ní Fhlannagáin <pidge@baylibre.com>
Signed-off-by: Piotr Łobacz <p.lobacz@welotec.com>
Signed-off-by: Jan Górski <j.gorski@welotec.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>