Do not raise from load_current_resource

- In order to actually be idempotent, the load_current_resource method
  which is called by all actions shouldn't raise if a volume that may
  have previously existed no longer exists.
Merge pull request #9 from rightscale-cookbooks/white_14_06_acu169749_load_current_resource_should_not_raise

Do not raise from load_current_resource