Extract merge process of the component options:

  * Move merge component's opts with distro, persona, etc to cfg.py
  * Implementing YamlMergeLoader
  * Add unit tests for correct updating cached and processed opts data
  * Add unit tests for YamlMergeLoader
  * Fix redefinition process in personas
  * Add documentation to YamlMergerLoader docstring

Change-Id: Ie491defca3df09d763081799d551cef8c2128701
Merge "Extract merge process of the component options:"