cli: Add tests for tns help

[rosen-vladimirov]

Add tests to verify CLI shows its help properly:

• tns -h should print the help
• tns --help should print the help
• tns <command> --help should print command's help
• Add test to verify tns dev-generate-help is working - this command should generate all the .html files of the help and it is used for our documentation. The generation of help can be broken by either changes in the code or changes in any help page. As CLI supports injecting code in the help pages, when the help is generated, in case the code in the help page is invalid, generation of html files will fail. So it is important to have a test that does the following:
  • remove <cli installation dir>/docs/html
  • execute tns dev-generate-help
  • ensure the exit code of the above mentioned command is 0.
  • ensures there are files in <cli installation dir>/docs/html.
• tns help should open browser (I know it is not easy to be tested, so this can be added in the future. For the moment we can just ensure CLI is not printing its command line help in this case.)