etcd pkg tests taking too long

The unit tests for the etcd package are reliably taking longer than 2s:

```
% ./test
Not on Linux - skipping fleet build
Building fleetctl...
Running tests...
ok  	github.com/coreos/fleet/agent	0.043s	coverage: 37.3% of statements
ok  	github.com/coreos/fleet/api	0.027s	coverage: 77.7% of statements
ok  	github.com/coreos/fleet/client	0.026s	coverage: 12.1% of statements
ok  	github.com/coreos/fleet/config	0.020s	coverage: 86.7% of statements
ok  	github.com/coreos/fleet/engine	0.025s	coverage: 34.1% of statements
ok  	github.com/coreos/fleet/etcd	2.289s	coverage: 85.5% of statements
ok  	github.com/coreos/fleet/event	0.010s	coverage: 100.0% of statements
ok  	github.com/coreos/fleet/fleetctl	0.028s	coverage: 21.7% of statements
ok  	github.com/coreos/fleet/job	0.022s	coverage: 71.4% of statements
ok  	github.com/coreos/fleet/machine	0.022s	coverage: 46.2% of statements
ok  	github.com/coreos/fleet/pkg	0.015s	coverage: 94.1% of statements
ok  	github.com/coreos/fleet/registry	0.039s	coverage: 24.2% of statements
ok  	github.com/coreos/fleet/sign	0.052s	coverage: 83.8% of statements
ok  	github.com/coreos/fleet/ssh	0.033s	coverage: 47.7% of statements
ok  	github.com/coreos/fleet/unit	0.021s	coverage: 76.6% of statements
Checking gofmt...
Success
```

This is unacceptable.
This is testing the inner workings of `crypto/tls`, which is not the responsibility of our tests.