juju/juju — pull request #962 by voidspace (2014-10-24 16:51:50+00:00)
Title: Cache results of checking for ec2 default vpc

The default-vpc of an ec2 account won't change during the lifetime of a jujud process (it requires days to change this), so we can cache the result and avoid round tripping to Amazon every time we need it's Id or to check for its existence.