Correct scenario specific results table headers

This patch allows to correct VM scenario command results displayed
when calling 'rally task detailed <uuid>' : command's result json
keys are now displayed.

Also add functional test to run in gates to check correct output.

Closes-Bug: #1328451

Change-Id: I7cf2a433e47779beba60c52d23825189e60f51a6
Merge "Correct scenario specific results table headers"