Fix destructive-cleanup failure when no old packages exist

When rpm -qa returns no packages, xargs would still invoke
rpm -e with no arguments, causing failure with "no packages
given for erase" (exit code 123).

Add -r flag to xargs to skip execution when input is empty.

Signed-off-by: Xiaofeng Wang <henrywangxf@me.com>

Author: henrywang

contrib/scripts/fedora-bootc-destructive-cleanup

@@ -5,7 +5,7 @@ set -xeuo pipefail
 
 # Remove all RPMs installed in the physical root (i.e. the previous OS)
 mount -o remount,rw /sysroot
-rpm -qa --root=/sysroot --dbpath=/usr/lib/sysimage/rpm | xargs rpm -e --root=/sysroot --dbpath=/usr/lib/sysimage/rpm
+rpm -qa --root=/sysroot --dbpath=/usr/lib/sysimage/rpm | xargs -r rpm -e --root=/sysroot --dbpath=/usr/lib/sysimage/rpm
 
 # Remove all container images (including the one that was used to install)
 # Note that this does not remove stopped containers, and so some storage