Updated Savanna part of the docs for Fuel 4.0

 * Changed all links to docs and artifacts from Savanna 0.2.2 to Savanna 0.3
 * Also added a sentence to make smooth transition between Additional Checks
   and Platform Tests sections

Change-Id: Ic31a8d79de121f57e8ee4c8099670dc4abf0dffa
Merge "Updated Savanna part of the docs for Fuel 4.0"