Do the basic configuration of the builtin logging module

Fixes #292
In a normal use case, `pip` would take care of configuring the logging
module as intended. But due to our intrusive import of pip internals,
that part wasn't properly done.

piptools/logging.py

@@ -1,8 +1,14 @@
 # coding: utf-8
 from __future__ import absolute_import, division, print_function, unicode_literals
 
+import logging
+
 from . import click
 
+# Initialise the builtin logging module for other component using it.
+# Ex: pip
+logging.basicConfig()
+
 
 class LogContext(object):
  def __init__(self, verbosity=0):