HPCC-19019 Return "roxie too busy" when RoxieControlLock fails.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>

common/roxiecommlib/roxiecommunicationclient.cpp

@@ -321,7 +321,7 @@ public:
     {
         unsigned start = msTick();
         if (!sendRoxieControlLock(sock, allOrNothing, wait))
-            throw MakeStringException(-1, "Roxie control:lock failed");
+            throw MakeStringException(-1, "Roxie is too busy (control:lock failed) - please try again later.");
         return sendRoxieControlQuery(sock, msg, remainingMsWait(wait, start));
     }
 

esp/clients/roxiecontrol.cpp

@@ -96,7 +96,7 @@ IPropertyTree *sendRoxieControlAllNodes(ISocket *sock, const char *msg, bool all
 {
     unsigned start = msTick();
     if (!sendRoxieControlLock(sock, allOrNothing, wait))
-        throw MakeStringException(-1, "Roxie control:lock failed");
+        throw MakeStringException(-1, "Roxie is too busy (control:lock failed) - please try again later.");
     return sendRoxieControlQuery(sock, msg, remainingMsWait(wait, start));
 }