[troubleshooting] hiera

Fix the display for note in 'Find the value hiera returns to puppet' doc part.

  * *note* -> .. note:: like other note in page http://spinal-stack.readthedocs.org/en/latest/deploy/introduction.html#requirements
  * `code` -> ``code`` (Display inline code https://pythonhosted.org/an_example_pypi_project/sphinx.html#code)