Support skipping reprepro wrapper via SKIP_REPREPRO_WRAPPER

If REPOS=... is unset by a custom script and only the release
steps should be executed, then without support for skipping the
reprepro_wrapper we end up with the Debian package being included
in $package-$distribution if $distribution is set or in $package
otherwise by default.  If those steps are unwanted you can now
set SKIP_REPREPRO_WRAPPER to either take care of the repository
inclusion yourself or running only through the release steps (if
$release is set accordingly).

Development sponsored by Sipwise GmbH, recorded as
TT#9830 in customers' ticket system.

scripts/build-and-provide-package

@@ -878,6 +878,11 @@ remove_missing_binary_packages() {
 }
 
 reprepro_wrapper() {
+  if [ -n "${SKIP_REPREPRO_WRAPPER:-}" ] ; then
+    echo "*** Skipping reprepro_wrapper as requested via SKIP_REPREPRO_WRAPPER ***"
+    return
+  fi
+
   if ! [ -d "$REPOSITORY" ] ; then
     bailout 1 "Error: repository ${REPOSITORY} does not exist."
   fi