Use a host specific memcache key for django_compressor

Otherwise all but one node in the HA cluster will miss
the static assets, causing ugliness and 404 messages in
the browser.

Fixes
https://bugzilla.novell.com/show_bug.cgi?id=894070
Merge pull request #185 from dirkmueller/master

Use a host specific memcache key for django_compressor