Fix UnicodeDecodeError for httplib

[moylop260]

Python 2.7.6 - /usr/lib/python2.7/httplib.py has the following code:

 820   def _send_output(self, message_body=None):
 821          """Send the currently buffered request and clear the buffer..."""
 826         self._buffer.extend(("", ""))
 827         msg = "\r\n".join(self._buffer)
 828         del self._buffer[:]
 829         # If msg and message_body are sent in a single send() call,
 830         # it will avoid performance problems caused by the interaction
 831         # between delayed ack and the Nagle algorithm.
 832         if isinstance(message_body, str):
 833             msg += message_body
 834             message_body = None
 835         self.send(msg)

If the variable self._buffer (line 827) has
[u'PUT /api/2/project/PROJECT/resource/RESOURCE/content/ HTTP/1.1', ...]
then msg variable is unicode string
but message_body is bytes string (line 832)
The line 833 concatenate unicode + bytes string and show the error:
Fix UnicodeDecodeError: 'ascii' codec can't decode byte ... in position ...: ordinal not in range(128)

Similar to:
python -c "u'unicode string' + 'bytes string é'"

Traceback (most recent call last):
  File "<input>", line 1, in <module>
    u'unicode string' + 'bytes string é'
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 13: ordinal not in range(128)

It's fixed forcing in host and url variables of transifex-client use bytes to concatenate bytes vs bytes.

Note: We are using from __future__ import unicode_literals