builder/amazon/all: address feedback for ami tag refactoring change

Use explicit name for Tag field and note tags added in the ui.
Update packer.go to cleanup plugin clients on exit. 

Since defer does not fire when exiting the application with os.Exit we need to be sure that we cleanup all of the clients on failures from the CLI and creating a new environment object.
Merge pull request #255 from johnbellone/patch-1

Update packer.go to cleanup plugin clients on bad CLI exit.
website: add myself to the community page