Remove dependency on skygw_utils.h

- STRERROR_BUFLEN moved to cdefs.h and renamed to MXS_STRERROR_BUFLEN.
  Better would be to provide a 'const char* mxs_strerror(int errno)'
  that would have a thread specific buffer for the error message.
- MIN and MAX also moved to defs.h as MXS_MIN and MXS_MAX.
- Now only mlist.h of the headers depend upon skygw_utils.h.

server/core/service.c

@@ -383,7 +383,7 @@ int serviceStartAllPorts(SERVICE* service)
             service->stats.n_failed_starts++;
             char taskname[strlen(service->name) + strlen("_start_retry_") +
                           (int) ceil(log10(INT_MAX)) + 1];
-            int retry_after = MIN(service->stats.n_failed_starts * 10, SERVICE_MAX_RETRY_INTERVAL);
+            int retry_after = MXS_MIN(service->stats.n_failed_starts * 10, SERVICE_MAX_RETRY_INTERVAL);
             snprintf(taskname, sizeof(taskname), "%s_start_retry_%d",
                      service->name, service->stats.n_failed_starts);
             hktask_oneshot(taskname, service_internal_restart,