manifests: consistently use set -xeuo pipefail in postprocess scripts

The `set -euo pipefail` shouldn't be controversial.

The `set -x` bit is more debatable because it makes
the output more verbose but I find it helpful right
now as I comb through all sorts of details as part of
https://github.com/coreos/fedora-coreos-tracker/issues/1861.

If we care about less verbose output, I'd prefer we keep `-x` but
switched to having rpm-ostree buffer postprocess output and only dump it
if it fails.

minimal/tmpfiles.yaml

@@ -1,6 +1,7 @@
 postprocess:
   - |
     #!/bin/bash
+    set -xeuo pipefail
     cat >/usr/lib/tmpfiles.d/bootc-base-rpmstate.conf <<'EOF'
     # Workaround for https://bugzilla.redhat.com/show_bug.cgi?id=771713
     d /var/lib/rpm-state 0755 - - -