Added warning message upon REST API failure for crash_gen tool

tests/pytest/crash_gen.py

@@ -561,9 +561,13 @@ class DbConnRest(DbConn):
         self.isOpen = False
 
     def _doSql(self, sql):
+        try:
             r = requests.post(self._url, 
                 data = sql,
                 auth = HTTPBasicAuth('root', 'taosdata'))            
+        except:
+            print("REST API Failure (TODO: more info here)")
+            raise
         rj = r.json()
         # Sanity check for the "Json Result"
         if (not 'status' in rj):