MXS-1553: Enforce SSL usage for monitors

If a server is configured to use SSL, then MaxScale should respect the
configuration and refuse to use a connection that is not encrypted.

server/core/server.c

@@ -140,6 +140,9 @@ SERVER* server_alloc(const char *name, const char *address, unsigned short port,
     server->created_online = false;
     server->charset = SERVER_DEFAULT_CHARSET;
 
+    // Log all warnings once
+    memset(&server->log_warning, 1, sizeof(server->log_warning));
+
     spinlock_acquire(&server_spin);
     server->next = allServers;
     allServers = server;