Fix HSS connectons on multi-core processors by only having one worker process.

On multi-core processors, Homestead previously spawned one Python process per core. This allowed HTTP connections to be handled faster, but broke HSS connections - each process made its own HSS connection with the same Origin-Host and Origin-Realm. The HSS only acknowledged one of these connections, causing most requests to fail.

This commit forces Homestead to use a single process (and therefore a single HSS connection) in order to fix this.
Merge pull request #89 from Metaswitch/fix-multicore-hss

[Reviewer: Matt] Fix HSS connections on multi-core processors