Use the knife.rb node_name as the default admin

When creating or updating a vault, ensure that
the knife.rb node_name is set as an admin. This
fixes the issue where you can create a vault that
cannot be modified or deleted without logging into
an authorized client and running a knife command.
Fix variable shadowing inside of the block
Merge pull request #93 from jgeiger/node_name_is_default_admin

knife.rb node name is default admin