Rename boto tests files to include '_test' at the end

Unit tests won't run unless '_test' is appended to the file name.

@colinbjohnson - Regarding your questions on salt-users, which I missed this detail before, you have to add `_test` to the name of your test file in order for the test runner to pick them up. The `_test` naming requirement is only applied to unit tests. It is not needed for integration tests. Sorry for the confusion there!