maas missing dependency on python-apt

[Scott Moser]

I did an upgrade from:
 1.7.0+bzr3299-0ubuntu3~trusty1 to 1.7.3+bzr3363-0ubuntu1~trusty1

And ended up with a non-working maas.

/var/log/apache2/error.log had messages like seen at http://paste.ubuntu.com/10868052/ .

cleaned up below:

mod_wsgi (pid=15642): Exception occurred processing WSGI script '/usr/share/maas/wsgi.py'.
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/django/core/handlers/wsgi.py", line 187, in __call__
    self.load_middleware()
  File "/usr/lib/python2.7/dist-packages/django/core/handlers/base.py", line 47, in load_middleware
    mw_instance = mw_class()
  File "/usr/lib/python2.7/dist-packages/maasserver/middleware.py", line 111, in __init__
    reverse('login'),
  File "/usr/lib/python2.7/dist-packages/django/core/urlresolvers.py", line 536, in reverse
    return iri_to_uri(resolver._reverse_with_prefix(view, prefix, *args, **kwargs))
  File "/usr/lib/python2.7/dist-packages/django/core/urlresolvers.py", line 403, in _reverse_with_prefix
    self._populate()
  File "/usr/lib/python2.7/dist-packages/django/core/urlresolvers.py", line 267, in _populate
    for pattern in reversed(self.url_patterns):
  File "/usr/lib/python2.7/dist-packages/django/core/urlresolvers.py", line 365, in url_patterns
    patterns = getattr(self.urlconf_module, "urlpatterns", self.urlconf_module)
  File "/usr/lib/python2.7/dist-packages/django/core/urlresolvers.py", line 360, in urlconf_module
    self._urlconf_module = import_module(self.urlconf_name)
  File "/usr/lib/python2.7/dist-packages/django/utils/importlib.py", line 40, in import_module
    __import__(name)
  File "/usr/share/maas/maas/urls.py", line 28, in <module>
    url(r'^', include('maasserver.urls')),
  File "/usr/lib/python2.7/dist-packages/django/conf/urls/__init__.py", line 26, in include
    urlconf_module = import_module(urlconf_module)
  File "/usr/lib/python2.7/dist-packages/django/utils/importlib.py", line 40, in import_module
    __import__(name)
  File "/usr/lib/python2.7/dist-packages/maasserver/urls.py", line 329, in <module>
    (r'^api/1\\.0/', include('maasserver.urls_api'))
  File "/usr/lib/python2.7/dist-packages/django/conf/urls/__init__.py", line 26, in include
    urlconf_module = import_module(urlconf_module)
  File "/usr/lib/python2.7/dist-packages/django/utils/importlib.py", line 40, in import_module
    __import__(name)
  File "/usr/lib/python2.7/dist-packages/maasserver/urls_api.py", line 101, in <module>
    from maasserver.api.version import VersionHandler
  File "/usr/lib/python2.7/dist-packages/maasserver/api/version.py", line 23, in <module>
    from maasserver.utils.version import get_maas_version_subversion
  File "/usr/lib/python2.7/dist-packages/maasserver/utils/version.py", line 21, in <module>
    import apt_pkg
ImportError: No module named apt_pkg