Refactor test_tag using pytest.mark.parametrize

    Parametrize tag creation, tagset creation and tag linking
Enforce long as type of tag id arguments
Fix integration test for tag/tagset creation with no description
Add unit tests for argument long type check

Move all CLI tag unit tests under test/unit/clitest/
Remove unnecessary subcommands variable
Improve object:id parsing in tag link subcommand and add unit tests
Clean up comment lines
Add integration tests for tag list and tag listsets commands
Fix clip() when input is None (empty description)
Merge pull request #1903 from sbesson/11817_tagcreateset

CLI tag plugin: bug fixes