etcdserver/etcdhttp: store location adjustment

Detailed adjustment:
/_etcd/machines/* -> /0/members/*
/* -> /1/*

And it keeps key path returned to user the same as before.

fixes #1331
I thought there would be a cleaner way to do it with iota, but I suppose not since there's no way to use it to create a string within the const. Sorry for the distraction @unihorn.