Add first set of tests for the CLI tag plugin

- Derive a CLITest class derived from ITest which creates a CLI and registers
the sessions control
- Add basic tests for help subcommands
Add integration tests to test tag/tagset creation via the CLI
Add integration test for tag load subcommand
Add integration test for tag link subcommand
Add integration tests for tag/tagset commands requiring user input

Use mox.StubOutWithMock() and mox.ReplayAll() to simulate raw_input
Move mox setup/teardown methods to the abstract CLITest class
Additional tests for tag link CLI subcommand
Add integration tests for tags/tagsets created with no --name argument
Refactor argument logic in clitest to reduce redundancy

- Define args as class attribute and set it to login_args() by default
- Add "tag" command to args in the setup_method
Check tagsets are created with NSINSIGHTTAGSET namespace
Merge pull request #1688 from sbesson/11466_tag_clitest

Add CLI tests for tag plugin