[2676] Error when missing ConfigManager

In the code before refactoring, when the CfgMgr wasn't there, it did a
SessionTimeout. Now the RPCRecipientMissing is raised instead, but as it
is subclass of RPCError, we need to exclude it from the error ignoring.

Actually, the error ignoring itself is very questionable thing, but it
is as it was before.

src/bin/stats/stats.py.in

@@ -253,6 +253,10 @@ class Stats:
         # 'show_processes' of Init
         try:
             value = self.mccs.rpc_call('show_processes', 'Init')
+        except isc.config.RPCRecipientMissing:
+            # This has been SessionTimeout before, so we keep the original
+            # behavior.
+            raise
         except isc.config.RPCError:
             # TODO: Is it OK to just pass? As part of refactoring, preserving
             # the original behaviour.