Disable IPv6 in Google Compute Engine

Not currently supported in the Google Compute Engine network, so except
for esoteric use cases there's no need to run the risk of software
handling this badly. With support in the kernel but missing in the
network, we've already seen one case of misleading error behavior that,
while not technically incorrect, made debugging more difficult.
Update gcutil to latest version
Merge branch 'master' of git://github.com/andsens/build-debian-cloud
Merge pull request #80 from google/master

Minor updates from June 17th Google Compute Engine images