all: reorganize "internal" Go packages

[gyuho]

Packages like "alarm" and "compactor" are not expected to be used outside of etcd project.

Move all internal packages under /internal/*.

[xiang90]

lease, mvcc, store should be moved too.

[gyuho]

@mitake Could you double-check if it's safe to move auth to internal/auth?

"github.com/coreos/etcd/auth" is not meant to be used directly by clients. All errors are converted to rpctypes, so moving to internal won't break anything (e.g. clients will still receives error typed rpctypes.ErrRoleAlreadyExist, not auth.ErrRoleAlreadyExist).

Also seems like there's no external project that imports "github.com/coreos/etcd/auth", based on github and Google search results.

[mitake]

@gyuho ok, I'll look at it

[mitake]

Moving the package to internal won't cause problems, I think. Should I create a PR for this? @gyuho

[gyuho]

@mitake Sure! Thanks!