Fixes bug with HA client in multi threading environments

HAClient would wrap Client methods with HA functionality, but did
this in the constructor. This caused wrapped methods to be wrapped
again when client.py was included multiple times.
This functionality has been moved to a classmethod that only
is called once on module load time.
Merge pull request #58 from spotify/wouter/dev

Fixes bug with HA client in multi threading environments
Bump debian to 2.4.1
Handle errors gracefully (config parse error, empty namenodes list)

1. If there's config parse error, catch it and print error message. Don't
stop the process, just print message.
2. If namenodes list for HAClient is empty throw exception in the
__init__ method, and print a sane error message.
3. If we find no namenodes in AutoConfigClient __init__ method throw
exception with a sane message.