fog/fog-core — pull request #33 by mountkin (2014-04-02 12:26:25+00:00)
Title: change the default interval to a proc that returns exponential interval

This PR is related to https://github.com/fog/fog-core/pull/18
The purpose is to make the ```wait_for``` method to accept a proc to determine the sleep interval.
According suggestions from most IaaS providers, the retry should use an exponential backoff algorithm. So I changed the default interval to a proc that returns exponential intervals for sleep.