Fix shell_plus --print-sql for django 1.7

https://github.com/django/django/blob/stable/1.7.x/django/db/backends/util.py
The django.db.backends.util module has been renamed.
Use django.db.backends.utils instead.
Fix runserver_plus --print-sql for django 1.7

https://github.com/django/django/blob/stable/1.7.x/django/db/backends/util.py
The django.db.backends.util module has been renamed.
Use django.db.backends.utils instead.
Merge pull request #525 from 9gix/bugfix/printsql-django17

--print-sql not working on Django 1.7