multi-query with ddl may need sync context

[irene-coming]

• dble version：
  5.6.29-dble-9.9.9.9-153cf8b-20180928075325
• preconditions ：
  no
• configs：

schema.xml

        <schema name="mytest" sqlMaxLimit="100" dataNode="dn5">
                <table name="aly_test" dataNode="dn1,dn2,dn3,dn4" rule="hash-four" />
        </schema>
        <dataNode name="dn1" dataHost="172.100.9.5" database="db1" />
        <dataNode name="dn2" dataHost="172.100.9.6" database="db1" />
        <dataNode name="dn3" dataHost="172.100.9.5" database="db2" />
        <dataNode name="dn4" dataHost="172.100.9.6" database="db2" />
        <dataNode name="dn5" dataHost="172.100.9.5" database="db3" />

• steps：
  step1. run ./multiQuery.o

source file and compile see autotest directory:
autotest/dble/tree/master/drivers/c_mysql_api/multi-queries

• expect result：
  1.print multi resultsets:
  0 rows affected
  More results exist
  0 rows affected
  More results exist
  0 rows affected
  More results exist
  0 rows affected
  More results exist
  1 rows affected
  More results exist
  1 rows affected
  More results exist
  0 rows affected

• real result：

  1. print multi resultsets:
     0 rows affected
     More results exist
     0 rows affected
     More results exist
     0 rows affected
     More results exist
     Could not get next result

• supplements：

  1. dble log segment

/label ~BUG

[yanhuqing666]

In multi-queries ，the previous query is a distribute transaction would cause the next query executed for two times

[yanhuqing666]

9acdbb8 not for #734 but #743

[irene-coming]

verified on version: 5.6.29-dble-9.9.9.9-9acdbb8-20180929073705
autotest:mysql_multi_queries.cpp