MXS-1506: Clean up various functions

Reduced variable scopes and removed unused code.

server/modules/routing/readwritesplit/rwbackend.cc

@@ -10,7 +10,8 @@ namespace maxscale
 RWBackend::RWBackend(SERVER_REF* ref):
     mxs::Backend(ref),
     m_reply_state(REPLY_STATE_DONE),
-    m_large_packet(false)
+    m_large_packet(false),
+    m_command(0)
 {
 }