JCLOUDS-703 missing imageSpaceGb from machineType

The machine types don't seem to be giving a value for imageSpaceGb.

It is not clear if this missing imageSpaceGb is just for my requests to the api or if 
this is happening to all users of the API. I have filed a bug with google to clarify 

https://code.google.com/p/google-compute-engine/issues/detail?id=111

In the mean time I am assuming that this is the case and the imageSpaceGb will 
no longer appear in the response. 

The missing imageSpaceGb means they get the value zero in MachineType 
and as a consequence the Hardware does not support an image and the simple 
`computeService.templateBuilder().smallest().build()`
fails to find a valid template.

However, google's documentation states that 'You must always specify an
image when you create an instance...'.

So it would seem sensible that the missing value for this is ignored and
supportsImage uses the alwaysTrue predicate.