Correctly close OHTable to avoid database credentials reused (#138)

* fix connection re-used between files because of incorrect close

* close all obTableClient when closing OHTable and clear cache

* patch fix database credential re-use bugfix to master

Author: JackShi148

src/main/java/com/alipay/oceanbase/hbase/OHTable.java

@@ -1457,6 +1457,7 @@ public void close() throws IOException {
         if (cleanupPoolOnClose) {
             executePool.shutdown();
         }
+        ObTableClientManager.clear();
     }
 
     @Override

src/main/java/com/alipay/oceanbase/hbase/util/ObTableClientManager.java

@@ -128,6 +128,17 @@ public static ObTableClient getOrCreateObTableClient(ObTableClientKey obTableCli
         return OB_TABLE_CLIENT_INSTANCE.get(obTableClientKey);
     }
 
+    public static void clear() throws IOException {
+        try {
+            for (Map.Entry<ObTableClientKey, ObTableClient> pair : OB_TABLE_CLIENT_INSTANCE.entrySet()) {
+                pair.getValue().close();
+            }
+        } catch (Exception e) {
+            throw new IOException("fail to close tableClient" , e);
+        }
+        OB_TABLE_CLIENT_INSTANCE.clear();
+    }
+
     public static class ObTableClientKey {
         private String     paramUrl;
         private String     fullUserName;