Template for scenario descriptor file (sdf) and an example

Template for scenario descriptor file (sdf) and an example

Patchset 1: Initial version
Patchset 2: Important comments resolved, adding info about
optional/mandatory, and better syntax for hardware options.
Patchset 3: Resolving comments. Some comments marked with #$$$$
where things need discussion on hackfest.
Patchset 4: more comments resoved, provided alternate syntax proposal
using role definitions for nodes to define ha and noha.
Patchset 5: small correction
Patchset 6: more comments resolved, changes discussed on hackfest done.

Jira OCTO-162

Change-Id: I54e3450f04e4dcb6bc9b5efa36f2c8aa3f7617b0
Signed-off-by: ulik <ulrich.kleber@huawei.com>