[FLINK-21887][sql-client] Add SHOW VIEWS test in CliClientITCase

[fsk119]

What is the purpose of the change

This is just do some code clean before unify the parser. Move the SHOW VIEWS test from the CliClientTest into CliClientITCase. It also removes some usesless codes

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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Automated Checks

Last check on commit 681e314 (Sat Mar 20 10:26:23 UTC 2021)

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[wuchong]

LGTM. I only have a minor comment.

[wuchong]

create view `default`.MyView..

To keep align with the above create table?

[wuchong]

LGTM.