test to upload rpm content to an existing repo

@Ichimonji10 : could you please review it once. I'm facing below issue, it looks like to me a bug in api's but still wanted to double check:

```
FAIL: @Test: Create a repository and upload rpm contents
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/sghai/QE/robottelo/tests/foreman/api/test_repository_v2.py", line 366, in test_positive_update_5
    status_code_error(path, status_code, response),
AssertionError: Desired HTTP 200 but received HTTP 500 after sending request to https://qe-sat6-rhel7.usersys.redhat.com:443/katello/api/v2/repositories/145/upload_content. [u"undefined method `path' for #<String:0x007f9f3d061330>"]
```

If you chunk up your test into sections like this, I find it really easy to read through. This isn't a blocker: just consider it a suggestion.

```python
def test_positive_update_5(self):
    """@Test: ...

    @Feature: ...

    @Assert: ...

    """
    repository_attrs = entities.Repository(...).create()

    # Upload an RPM file
    path = entities.Repository(...).path(...)
    response = client.post(...)
    status_code = httplib.OK
    self.assertEqual(...)

    # Fetch the updated repository
    updated_attrs = entities.Repository(...)

    # Assert that the content count has been updated
    self.assertEqual(...)
```