XA datasource shouldn't require all cases working in a global transaction context

- [ ] I have searched the [issues](https://github.com/seata/seata/issues) of this repository and believe that this is not a duplicate.

### Ⅰ. Issue Description

Unexpected error was thrown when using XA mode with XA datasource proxy.

Just a select sql which is not intending to work with XA transaction.

### Cause: java.sql.SQLException: failed to register xa branch null since GlobalTransactionNotExist:Response[ TransactionException[Could not found global transaction xid = null, may be has finished.] ]
; uncategorized SQLException for SQL []; SQL state [null]; error code [0]; failed to register xa branch null since GlobalTransactionNotExist:Response[ TransactionException[Could not found global transaction xid = null, may be has finished.] ]; nested exception is java.sql.SQLException: failed to register xa branch null since GlobalTransactionNotExist:Response[ TransactionException[Could not found global transaction xid = null, may be has finished.] ]] with root cause
io.seata.core.exception.RmTransactionException: Response[ TransactionException[Could not found global transaction xid = null, may be has finished.] ]
at io.seata.rm.AbstractResourceManager.branchRegister(AbstractResourceManager.java:69) ~[seata-all-1.2.0.jar:1.2.0]
at io.seata.rm.DefaultResourceManager.branchRegister(DefaultResourceManager.java:96) ~[seata-all-1.2.0.jar:1.2.0]
at io.seata.rm.datasource.xa.ConnectionProxyXA.setAutoCommit(ConnectionProxyXA.java:133) ~[seata-all-1.2.0.jar:1.2.0]
at io.seata.rm.datasource.xa.ExecuteTemplateXA.execute(ExecuteTemplateXA.java:41) ~[seata-all-1.2.0.jar:1.2.0]
at io.seata.rm.datasource.xa.PreparedStatementProxyXA.execute(PreparedStatementProxyXA.java:66) ~[seata-all-1.2.0.jar:1.2.0]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_191-1-redhat]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_191-1-redhat]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_191-1-redhat]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_191-1-redhat]
at org.apache.ibatis.logging.jdbc.PreparedStatementLogger.invoke(PreparedStatementLogger.java:59) ~[mybatis-3.4.5.jar:3.4.5]
at com.sun.proxy.$Proxy268.execute(Unknown Source) ~[na:na]
at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:63) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83) ~[mybatis-3.4.5.jar:3.4.5]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_191-1-redhat]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_191-1-redhat]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_191-1-redhat]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_191-1-redhat]
at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) ~[mybatis-3.4.5.jar:3.4.5]
at com.github.pagehelper.SqlUtil._processPage(SqlUtil.java:351) ~[pagehelper-4.0.1.jar:na]
at com.github.pagehelper.SqlUtil.processPage(SqlUtil.java:329) ~[pagehelper-4.0.1.jar:na]
at com.github.pagehelper.PageHelper.intercept(PageHelper.java:150) ~[pagehelper-4.0.1.jar:na]
at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.4.5.jar:3.4.5]
at com.sun.proxy.$Proxy266.query(Unknown Source) ~[na:na]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) ~[mybatis-3.4.5.jar:3.4.5]
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77) ~[mybatis-3.4.5.jar:3.4.5]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_191-1-redhat]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_191-1-redhat]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_191-1-redhat]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_191-1-redhat]
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) ~[mybatis-spring-1.3.1.jar:1.3.1]
at com.sun.proxy.$Proxy141.selectOne(Unknown Source) ~[na:na]
at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:166) ~[mybatis-spring-1.3.1.jar:1.3.1]
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:82) ~[mybatis-3.4.5.jar:3.4.5]

### Ⅱ. Describe what happened

If there is an exception, please attach the exception trace:

```
Just paste your stack trace here!
```

### Ⅲ. Describe what you expected to happen

### Ⅳ. How to reproduce it (as minimally and precisely as possible)

1. xxx
2. xxx
3. xxx

### Ⅴ. Anything else we need to know?

### Ⅵ. Environment:

- JDK version :
- OS :
- Others: