infoschema,executor: add PROCESSLIST table to INFORMMATION_SCHEMA database

[tiancaiamao]

What have you changed? (mandatory)

add PROCESSLIST table to INFORMMATION_SCHEMA database
Basically, it's the same with show processlist

mysql> select * from processlist;
+------+------+-----------+--------------------+---------+------+-------+---------------------------+
| ID   | USER | HOST      | DB                 | COMMAND | TIME | STATE | Info                      |
+------+------+-----------+--------------------+---------+------+-------+---------------------------+
|    1 | root | 127.0.0.1 | information_schema | Query   |    0 | 2     | select * from processlist |
+------+------+-----------+--------------------+---------+------+-------+---------------------------+
1 row in set (0.00 sec)

What is the type of the changes? (mandatory)

• Improvement (non-breaking change which is an improvement to an existing feature)

How has this PR been tested? (mandatory)

manually

Does this PR affect documentation (docs/docs-cn) update? (mandatory)

no

Does this PR affect tidb-ansible update? (mandatory)

no

Does this PR need to be added to the release notes? (mandatory)

no

@coocood @jackysp

[coocood]

LGTM

[lysu]

/run-all-tests

[lysu]

/run-mybatis-test

[lysu]

LGTM

[zz-jason]

@tiancaiamao Please add some genius-labels for this PR 😄