stx-metal: add kickstart fixes for poky-stx

Add a patch for the ks templates to fix several issues for poky-stx:
- Fix for creating DNF repo
- Add a pre script to adjust the directories
- Add extra users and groups
- Add installer images for pxe-network-installer
- Fix the grub command: grub2 -> grub
- Adjust the pkglist for poky-stx

Issue-ID: INF-142
Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Change-Id: Ib572f534c256d3692ad2ac7dce4cdcb16839a9b0