Satellite 5 / Proxy 5, yum-rhn-plugin and HTTPD whitespace: "[Errno 14] HTTP Error 400 - Bad Request" on client and "request failed: error reading the headers" on server logs

Issue

• Traceback error from client systems caused by receiving an “HTTP Error 400” response from the Satellite or Proxy 5 server, such as this:

# tail /var/log/up2date    
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1685, in _getRepoXML
    self._loadRepoXML(text=self.ui_id)
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1676, in _loadRepoXML
    return self._groupLoadRepoXML(text, self._mdpolicy2mdtypes())
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1650, in _groupLoadRepoXML
    if self._commonLoadRepoXML(text):
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1470, in _commonLoadRepoXML
    result = self._getFileRepoXML(local, text)
  File "/usr/lib/python2.7/site-packages/yum/yumRepo.py", line 1248, in _getFileRepoXML
    size=102400) # setting max size as 100K
  File "/usr/share/yum-plugins/rhnplugin.py", line 399, in _getFile
    start, end, copy_local, checkfunc, text, reget, cache, size)
  File "/usr/share/yum-plugins/rhnplugin.py", line 501, in _noExceptionWrappingGet
    raise urlException
<class 'yum.Errors.RepoError'>: failed to retrieve repodata/repomd.xml from rhel-x86_64-server-7
error was [Errno 14] HTTP Error 400 - Bad Request

• With the following error message in server-side Satellite or Proxy 5 Apache logs:

# tail /var/log/httpd/error_log 
[Wed Feb 15 07:37:56 2017] [error] [client 10.10.10.10] request failed: error reading the headers