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
If readability is a goal, consider something like this:

```python
# Step 1: Check whether the config file contains main.project
robottelo_mode = ...
if robottelo_mode is None:
    raise ProjectModeError(...)

# Step 2: Check whether the config file value is sane
robottelo_mode = robottelo_mode.lower()
if robottelo_mode not in ALLOWED_PROJECT_MODES:
    raise ProjectModeError(...)

# Config file option exists and is sane. Use it.
return unittest.skipIf(...)
```

Doing this allows the code to be in line with [The Zen of Python](http://legacy.python.org/dev/peps/pep-0020/): "Flat is better than nested."

So, this my suggestion still stands, though I'm not going to block on it.