Use system.getHostname() everywhere
Replace os.environ['HTTP_HOST'] with system.getHostname(), as a
result we do not crash when 'HTTP_HOST' is unset now.
from django.contrib import admin
from django.contrib.sites.models import Site
class SiteAdmin(admin.ModelAdmin):
list_display = ('domain', 'name')
search_fields = ('domain', 'name')
admin.site.register(Site, SiteAdmin)