Fixes to minor Coverity errors:

75424
73422
72724
72702
72662

server/core/gateway.c

@@ -1479,7 +1479,11 @@ int main(int argc, char **argv)
 		bool succp;
 
                 sprintf(buf, "%s/log", home_dir);
-                mkdir(buf, 0777);
+				if(mkdir(buf, 0777) != 0){
+					fprintf(stderr,
+							"Error: Cannot create log directory: %s\n",buf);
+					goto return_main;
+				}
                 argv[0] = "MaxScale";
                 argv[1] = "-j";
                 argv[2] = buf;