Closes issue #1475
The command line tool that uses this endpoint -> https://github.com/kolide/configimporter
* Added support for atomic imports and dry run imports
* Added code so that imports are idempotent
Notable refactoring:
- Use stdlib "context" in place of "golang.org/x/net/context"
- Go-kit no longer wraps errors, so we remove the unwrap in transport_error.go
- Use MakeHandler when setting up endpoint tests (fixes test bug caught during
this refactoring)
Closes#1411.
