Remove automated skip decsion from compute

* The automated skip decisions are expensive, it is visible
  if you just run a single test case.

* The automated skip decisions are not fully trusted, so we should avoid them.

* Adding the flavor extra configuration option to the configuration file
 until we cannot move to test case attribute based test selection.

* Adding the CLI section to the tempest.conf.sample

Change-Id: I81a408392a8de38b694b3132572b6e48700595a3
Merge "Remove automated skip decsion from compute"