Fix ConfigDBConnector import in pg-drop script

[vaibhavhd]

What I did

202012 PR tests are failing consistently. The failure is seen in tests/pgdropstat_test.py This is a new test that was originally added to master branch, and cherrypicked into 202012 where it started failing.

Related PR: #1678

2021-08-23T23:50:55.1608995Z =================================== FAILURES ===================================
2021-08-23T23:50:55.1609597Z __________________ TestPgDropstat.test_show_pg_drop_disabled ___________________
2021-08-23T23:50:55.1609973Z 
2021-08-23T23:50:55.1610710Z self = <tests.pgdropstat_test.TestPgDropstat object at 0x7f689981f7f0>
2021-08-23T23:50:55.1611229Z replace_config_db_file = None
2021-08-23T23:50:55.1624925Z 
2021-08-23T23:50:55.1626293Z     def test_show_pg_drop_disabled(self, replace_config_db_file):
2021-08-23T23:50:55.1626874Z         runner = CliRunner()
2021-08-23T23:50:55.1627308Z     
2021-08-23T23:50:55.1628750Z         result = runner.invoke(show.cli.commands["priority-group"].commands["drop"].commands["counters"])
2021-08-23T23:50:55.1629388Z >       assert result.exit_code == 0
2021-08-23T23:50:55.1630728Z E       assert 1 == 0
2021-08-23T23:50:55.1631207Z E        +  where 1 = <Result SystemExit(1)>.exit_code
2021-08-23T23:50:55.1631485Z 
2021-08-23T23:50:55.1632595Z tests/pgdropstat_test.py:61: AssertionError
2021-08-23T23:50:55.1633753Z ---------------------------- Captured stdout setup -----------------------------
2021-08-23T23:50:55.1634187Z SETUP
2021-08-23T23:50:55.1634795Z ----------------------------- Captured stderr call -----------------------------
2021-08-23T23:50:55.1635276Z Traceback (most recent call last):
2021-08-23T23:50:55.1635897Z   File "/__w/1/s/scripts/pg-drop", line 262, in <module>
2021-08-23T23:50:55.1636500Z     main()
2021-08-23T23:50:55.1637067Z   File "/__w/1/s/scripts/pg-drop", line 249, in main
2021-08-23T23:50:55.1637487Z     pgdropstat = PgDropStat()
2021-08-23T23:50:55.1638067Z   File "/__w/1/s/scripts/pg-drop", line 50, in __init__
2021-08-23T23:50:55.1638505Z     self.configdb = ConfigDBConnector()
2021-08-23T23:50:55.1639184Z   File "/usr/lib/python3/dist-packages/swsscommon/swsscommon.py", line 1961, in __init__
2021-08-23T23:50:55.1639761Z     super(ConfigDBConnector, self).__init__(use_unix_socket_path = use_unix_socket_path, namespace = namespace)
2021-08-23T23:50:55.1640531Z   File "/usr/lib/python3/dist-packages/swsscommon/swsscommon.py", line 1576, in __init__
2021-08-23T23:50:55.1641118Z     super(SonicV2Connector, self).__init__(use_unix_socket_path = use_unix_socket_path, netns = namespace)
2021-08-23T23:50:55.1641661Z TypeError: super(type, obj): obj must be an instance or subtype of type
2021-08-23T23:50:55.1642245Z ____________________ TestPgDropstat.test_show_pg_drop_show _____________________

The import mechanism for ConfigDBConnector is incorrect and that fails the PR tests on 202012 branch. The tests succeed on master branch with the original change.

2021-08-23T23:50:55.1657204Z ----------------------------- Captured stderr call -----------------------------
2021-08-23T23:50:55.1657678Z Traceback (most recent call last):
2021-08-23T23:50:55.1659116Z   File "/__w/1/s/scripts/pg-drop", line 262, in <module>
2021-08-23T23:50:55.1659555Z     main()
2021-08-23T23:50:55.1660096Z   File "/__w/1/s/scripts/pg-drop", line 249, in main
2021-08-23T23:50:55.1660515Z     pgdropstat = PgDropStat()
2021-08-23T23:50:55.1661104Z   File "/__w/1/s/scripts/pg-drop", line 50, in __init__
2021-08-23T23:50:55.1662374Z     self.configdb = ConfigDBConnector()
2021-08-23T23:50:55.1663359Z   File "/usr/lib/python3/dist-packages/swsscommon/swsscommon.py", line 1961, in __init__
2021-08-23T23:50:55.1666325Z     super(ConfigDBConnector, self).__init__(use_unix_socket_path = use_unix_socket_path, namespace = namespace)
2021-08-23T23:50:55.1667593Z   File "/usr/lib/python3/dist-packages/swsscommon/swsscommon.py", line 1576, in __init__
2021-08-23T23:50:55.1671490Z     super(SonicV2Connector, self).__init__(use_unix_socket_path = use_unix_socket_path, netns = namespace)
2021-08-23T23:50:55.1672194Z TypeError: super(type, obj): obj must be an instance or subtype of type
2021-08-23T23:50:55.1712428Z ____________________ TestPgDropstat.test_show_pg_drop_clear ____________________

How I did it

Update ConfigDBConnector import from swss-common to swsssdk.

How to verify it

PR tests for 202012 target branch are passing now.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[qiluo-msft]

I prefer #1780 to fix the exact issue. Pending decision on that.

[qiluo-msft]

Close in favor of #1780

[lguohan]

since #1780 is merged,