Always using client side timestamp

["fan1emon@outlook.com" <fa...@outlook.com>]

Hey guys,

I'm using phoenix 5.1.2;

When execute query 'upsert into ... values' on a table without any timestamp row, the cell timestamp in hbase will be set to the one on client side.

```sql
create table students(id interger primary key, name varchar);
upsert into students values(1, 'id1');
```

and scan in hbase shell
```shell
scan 'STUDENTS'
```

the timestamp is client side.

Is that the expected behavior?
The client timestamp is not always sync to the server.
This will cause upsert not work when client delete data.
Since delete will use server side timestamp.

Any properties can help? 
I read the code in upsert and find that UpsertValuesMutationPlan may set the wrong `useServerTimestamp`




fan1emon@outlook.com