chore(build): use third_party.go

use the third_party.go project to replace our update script. This
requires moving a few things around and gets rid of a few annoying bugs:

- You can now bump individual packages
- A new src directory isn't created on build
- Less shell scripting!
- Things get built into ./bin/

.gitignore

@@ -1,7 +1,5 @@
-src/
 pkg/
-/etcd
-/etcdbench
 /server/release_version.go
 /go-bindata
 /machine*
+/bin