feat(mkosi): Use packaged `signstar-configure-build` for build

Fixes: #119


Signed-off-by: David Runge <dvzrv@archlinux.org>

resources/mkosi/signstar/mkosi.conf

@@ -21,6 +21,7 @@ Packages=
 	linux-hardened
 	nftables
 	openssh
+	signstar-configure-build
 	systemd
 RemoveFiles=
 	/.gnupg

resources/mkosi/signstar/mkosi.postinst.chroot

@@ -2,13 +2,11 @@
 
 set -Eeuo pipefail
 
-export PATH="$PATH:/usr/local/bin"
+export PATH="/usr/local/bin:$PATH"
 
-if command -v signstar-configure-build > /dev/null; then
-  printf "Configure users...\n"
-  signstar-configure-build --version
-  signstar-configure-build
-fi
+printf "Configure users...\n"
+signstar-configure-build --version
+signstar-configure-build
 
 printf "Setup resolv.conf\n"
 ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf