IMPALA-13642: Fix unused test vector in test_scanners.py

Several test vectors were ignored in test_scanners.py. This cause
repetition of the same test without actually varying the test
exec_option nor debug_action.

This patch fix it by:
- Use execute_query() instead of client.execute()
- Passing vector.get_value('exec_option') when executing test query.

Repurpose ImpalaTestMatrix.embed_independent_exec_options to deepcopy
'exec_option' dimension during vector generation. Therefore, each test
execution will have unique copy of 'exec_option' for them self.

This patch also adds flake8-unused-arguments plugin into
critique-gerrit-review.py and py3-requirements.txt so we can catch this
issue during code review. impala-flake8 is also updated to use
impala-python3-common.sh. Adds flake8==3.9.2 in py3-requirements.txt,
which is the highest version that has compatible dependencies with
pylint==2.10.2.

Drop unused 'dryrun' parameter in get_catalog_compatibility_comments
method of critique-gerrit-review.py.

Testing:
- Run impala-flake8 against test_scanners.py and confirm there is no
  more unused variable.
- Run and pass test_scanners.py in core exploration.

Change-Id: I3b78736327c71323d10bcd432e162400b7ed1d9d
Reviewed-on: http://gerrit.cloudera.org:8080/22301
Reviewed-by: Michael Smith <michael.smith@cloudera.com>
Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

infra/python/deps/py3-requirements.txt

@@ -30,3 +30,7 @@ pylint == 2.10.2
   platformdirs == 2.4.1
   typing-extensions == 3.10.0.2
 k5test==0.10.3
+
+# Below are needed only for dev
+flake8==3.9.2
+flake8-unused-arguments==0.0.13