Bail on Katello systems.

Katello breaks EL systems to the point where migrate2rocky can't properly
migrate them and any attempt to do so causes major corruption.  This prevents
migrate2rocky from running on Katello systems.

migrate2rocky.sh

@@ -103,6 +103,12 @@ pkg_ver() (
     return 0
 )
 
+pre_check () {
+    if [[ -e /etc/rhsm/ca/katello-server-ca.pem ]]; then
+	exit_message "Migration from Katello-modified systems is not supported by migrate2rocky."
+    fi
+}
+
 # All of the binaries used by this script are available in a EL8 minimal install
 # and are in /bin, so we should not encounter a system where the script doesn't
 # work unless it's severly broken.  This is just a simple check that will cause