Run postinst during rootfs generation

Background

In poky we have 2 types of postinst scripts: one (type-1) can be (and has already been) run at rootfs generation time and the other (type-2) has to be delayed to the first-boot of target device. Type-2 makes target device's first-boot slow and it would be great if we can fix it and convert it to type-1.

tasks

• We can instrument a first-boot with minimal/sato first to see which postinstalls take the most time and then prioritise those ones to fix.

• Dexuan has figurerd out a list of 33 recipes in total(recipes with the same name but with different versions are counted once) we possibly need to fix. For the recipes, we need try to find recipe-specific ways(use appropriately modified native utilities to generate caches, files, etc as necessary on the target filesystem).

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11 recipes: these could be easily fixed since Scott Garman has added the properly-adjusted utilities "adduser, addgroup, pwconv, etc". The owners of the recipes can help to fix them.

   meta/recipes-devtools/distcc/distcc_2.18.3.bb
   meta/recipes-extended/cronie/cronie_1.4.7.bb
   meta/recipes-extended/at/at_3.1.12.bb:47
   meta/recipes-support/hal/hal.inc:45
   meta/recipes-core/dbus/dbus.inc:49
   meta/recipes-connectivity/openssh/openssh_5.8p2.bb
   meta/recipes-connectivity/ppp-dialin/ppp-dialin_0.1.bb
   meta/recipes-graphics/x11-common/xserver-nodm-init.bb
   meta/recipes-multimedia/pulseaudio/pulseaudio.inc:87
   meta/recipes-extended/shadow/shadow_4.1.4.3.bb:125
   meta/classes/libc-package.bbclass