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/debugcli/debugcmd.c

@@ -1051,7 +1051,7 @@ execute_cmd(CLI_SESSION *cli)
         }
     }
     *lptr = 0;
-    args[MIN(MAXARGS - 1, i + 1)] = NULL;
+    args[MXS_MIN(MAXARGS - 1, i + 1)] = NULL;
 
     if (args[0] == NULL || *args[0] == 0)
     {
@@ -1964,9 +1964,9 @@ static void fail_accept(
     char* arg1,
     char* arg2)
 {
-    int failcount = MIN(atoi(arg2), 100);
+    int failcount = MXS_MIN(atoi(arg2), 100);
     fail_accept_errno = atoi(arg1);
-    char errbuf[STRERROR_BUFLEN];
+    char errbuf[MXS_STRERROR_BUFLEN];
 
     switch(fail_accept_errno) {
     case EAGAIN: