Description of problem:
The recent upgrade of python-request broke using of http over unix socket.
e.g. url is 'http+unix://%2Fvar%2Frun%2Fsecrets.socket/secrets/'

  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 535, in post                         
    return self.request('POST', url, data=data, json=json, **kwargs)                                      
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 474, in request                      
    prep = self.prepare_request(req)                                                                      
  File "/usr/lib/python2.7/site-packages/requests/sessions.py", line 407, in prepare_request              
    hooks=merge_hooks(request.hooks, self.hooks),                                                         
  File "/usr/lib/python2.7/site-packages/requests/models.py", line 302, in prepare                        
    self.prepare_url(url, params)                                                                         
  File "/usr/lib/python2.7/site-packages/requests/models.py", line 372, in prepare_url                    
    raise InvalidURL('URL has an invalid label.')                                                         
InvalidURL: URL has an invalid label.


The host part of url validation failed because of % and / are invalid code points in uts46 / IDNA 2008

Version-Release number of selected component (if applicable):
python2-requests 2.12.1-1.fc26

How reproducible:
Deterministic

Steps to Reproduce:
    def test_url_passthrough(protocol, url):
        session = requests.Session()
        session.mount(protocol, HTTPAdapter())
        p = requests.Request('GET', url=url)
        p.prepare()
        assert p.url == url
    
    test_url_passthrough("http+unix://", b"http+unix://%2Fvar%2Frun%2Fsocket/path")
   


Additional info:
Here is a related pull request
https://github.com/kennethreitz/requests/pull/3713

Please backport it after merge.