WireCloud should not respond with an error 500 to SuspiciousOperation errors

[aarranz]

WireCloud should not respond with a 500 error code response when a suspicious operation exception is raised (e.g. when a requests with an invalid HOST header arrives the service). Instead it should return a 400 error code response. This fix should be available when using Django 1.7-1.9 (Django 1.6 automatically uses a 500 error response, so we cannot fix it).

Also would be great to document how to silence a particular type of SuspiciousOperation. See the Django documentation for more info.

[aarranz]

Traceback:

File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_exception_response
  92.                 response = callback(request, **dict(param_dict, exception=exception))

File "/usr/local/lib/python2.7/dist-packages/django/utils/decorators.py" in _wrapped_view
  149.                     response = view_func(request, *args, **kwargs)

File "/usr/local/lib/python2.7/dist-packages/django/views/defaults.py" in bad_request
  79.     return http.HttpResponseBadRequest(template.render())

File "/usr/local/lib/python2.7/dist-packages/django/template/backends/django.py" in render
  95.             return self.template.render(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in render
  206.                     return self._render(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in _render
  197.         return self.nodelist.render(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in render
  992.                 bit = node.render_annotated(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in render_annotated
  959.             return self.render(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/loader_tags.py" in render
  173.         return compiled_parent._render(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in _render
  197.         return self.nodelist.render(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in render
  992.                 bit = node.render_annotated(context)

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in render_annotated
  959.             return self.render(context)

File "/usr/local/lib/python2.7/dist-packages/wirecloud/platform/templatetags/wirecloudtags.py" in render
  46.             context['THEME'] = context['THEME_ACTIVE']

File "/usr/local/lib/python2.7/dist-packages/django/template/context.py" in __getitem__
  77.         raise KeyError(key)