Manifest mock, and fixed tests.foreman.cli.test_subscription

Usage:

You need to have ```manifest.key_url```, ```manifest.fake_url``` and ```manifest.cert_url``` set in your robottelo.properties

My config can be found on:
http://pastebin.test.redhat.com/230135 

With updated config try

```nosetests -c robottelo.properties tests.foreman.cli.test_subscription```

and it should run :)
How about un-indenting each block of code after the relevant file is read? For example:

```python
with open(key_file) as handle:
    key = RSA.importKey(handle.read())
signature = PKCS1_v1_5.new(key)
with open(file_to_sign, "rb") as handle:
    digest = SHA256.new(handle.read())
return signature.sign(digest)
```