test: introduce test script

Why do this? `go test ./...` has a ton of annoying output:

```
?   	github.com/coreos/etcd	[no test files]
?   	github.com/coreos/etcd/crc	[no test files]
?   	github.com/coreos/etcd/elog	[no test files]
?   	github.com/coreos/etcd/error	[no test files] ok  
github.com/coreos/etcd/etcdserver	0.267s ok  
github.com/coreos/etcd/etcdserver/etcdhttp	0.022s
?   	github.com/coreos/etcd/etcdserver/etcdserverpb	[no test files] ok  
github.com/coreos/etcd/raft	0.157s
?   	github.com/coreos/etcd/raft/raftpb	[no test files] ok  
github.com/coreos/etcd/snap	0.018s
?   	github.com/coreos/etcd/snap/snappb	[no test files] 
third_party/code.google.com/p/gogoprotobuf/proto/testdata/test.pb.go:1234: 
undefined: __emptyarchive__.Extension ok  	github.com/coreos/etcd/store
4.247s ok github.com/coreos/etcd/third_party/code.google.com/p/go.net/context 
2.724s FAIL 
github.com/coreos/etcd/third_party/code.google.com/p/gogoprotobuf/proto
[build failed] ok 
github.com/coreos/etcd/third_party/github.com/stretchr/testify/assert 0.013s 
ok  	github.com/coreos/etcd/wait	0.010s ok  
github.com/coreos/etcd/wal	0.024s
?   	github.com/coreos/etcd/wal/walpb	[no test files]
```

And we have no had to manually configure drone.io which I want to avoid: 
https://drone.io/github.com/coreos/etcd/admin
@xiangli-cmu Fixed in 91c5263