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/modules/routing/avro/avro.c

@@ -411,7 +411,7 @@ createInstance(SERVICE *service, char **options)
                 }
                 else if (strcmp(options[i], "start_index") == 0)
                 {
-                    first_file = MAX(1, atoi(value));
+                    first_file = MXS_MAX(1, atoi(value));
                 }
                 else
                 {
@@ -1037,7 +1037,7 @@ void converter_func(void* data)
 
     if (binlog_end == AVRO_LAST_FILE)
     {
-        router->task_delay = MIN(router->task_delay + 1, AVRO_TASK_DELAY_MAX);
+        router->task_delay = MXS_MIN(router->task_delay + 1, AVRO_TASK_DELAY_MAX);
         add_conversion_task(router);
         MXS_INFO("Stopped processing file %s at position %lu. Waiting until"
                  " more data is written before continuing. Next check in %d seconds.",
@@ -1060,7 +1060,7 @@ static bool ensure_dir_ok(const char* path, int mode)
 
     if (path)
     {
-        char err[STRERROR_BUFLEN];
+        char err[MXS_STRERROR_BUFLEN];
         char resolved[PATH_MAX + 1];
         const char *rp = realpath(path, resolved);