Initial proposal to differentiate sam only and sat only tests

Now tests can use decorators to run/skip tests basead on server modes:
- runIf('sam') - runs only on sam server
- runIf('sat') - runs only on sat server
- no decoractor - runs on all server modes
Good catch. There are several cases in which `robottelo.properties` does not exist, such as when Travis or Sphinx & ReadTheDocs run.