Overwrite .rpmdb for debian updatevm

Resolves issue where the dom0 rpm database does not get used on
successive calls to qubes-dom0-update for debian updatevms.

Also resolves "cannot remove .rpmdbold.####" occurrences.

qubesos/qubes-issues#6124

package-managers/qubes-download-dom0-updates.sh

@@ -76,7 +76,8 @@ if [ -e /etc/debian_version ]; then
     # Default rpm configuration on Debian uses ~/.rpmdb for rpm database (as
     # rpm isn't native package manager there)
     mkdir -p "$DOM0_UPDATES_DIR$HOME"
-    ln -nsf "$DOM0_UPDATES_DIR/var/lib/rpm" "$DOM0_UPDATES_DIR$HOME/.rpmdb"
+    rm -rf "$DOM0_UPDATES_DIR$HOME/.rpmdb"
+    cp -r "$DOM0_UPDATES_DIR/var/lib/rpm" "$DOM0_UPDATES_DIR$HOME/.rpmdb"
 fi
 # Rebuild rpm database in case of different rpm version
 rm -f $DOM0_UPDATES_DIR/var/lib/rpm/__*