[Starcluster] Misleading Error Message on createvolume

[Austin Godber]

Howdy,
     There is a somewhat misleading error when using invalid credentials 
with "starcluster createvolume".  If you have invalid credentials (like 
deleting the last character off your secret key) the message will be:
     cli.py:1079 - ERROR - zone us-east-1c does not exist
rather than something like:
     ERROR - SignatureDoesNotMatch:

I am not using the latest git version though, 0.91

Austin