BF: do not rely on long relative path to upstairs config - symlink common.conf

fail2ban/tests/config/filter.d/common.conf

@@ -0,0 +1 @@
+../../../../config/filter.d/common.conf

fail2ban/tests/config/filter.d/zzz-generic-example.conf

@@ -6,8 +6,9 @@
 [INCLUDES]
 
 # Read common prefixes. If any customizations available -- read them from
-# common.local
-before = ../../../../config/filter.d/common.conf
+# common.local.  common.conf is a symlink to the original common.conf and
+# should be copied (dereferenced) during installation
+before = common.conf
 
 [Definition]