Fix possible data race in geard deployment test

Fixes the following data race found by `go test -race`:

```
WARNING: DATA RACE
Write by goroutine 28:
  sync.raceWrite()
      /usr/lib/golang/src/pkg/sync/race.go:41 +0x35
  sync.(*WaitGroup).Wait()
      /usr/lib/golang/src/pkg/sync/waitgroup.go:120 +0x16d
  net/http/httptest.(*Server).Close()
      /usr/lib/golang/src/pkg/net/http/httptest/server.go:168 +0x6a
  github.com/openshift/geard/deployment.TestNewDeploymentFromURL_Timeout()
      /data/src/github.com/openshift/geard/deployment/deployment_test.go:467 +0x1a5
  testing.tRunner()
      /usr/lib/golang/src/pkg/testing/testing.go:391 +0x10f

Previous read by goroutine 32:
  sync.raceRead()
      /usr/lib/golang/src/pkg/sync/race.go:37 +0x35
  sync.(*WaitGroup).Add()
      /usr/lib/golang/src/pkg/sync/waitgroup.go:60 +0xc1
  net/http/httptest.(*waitGroupHandler).ServeHTTP()
      /usr/lib/golang/src/pkg/net/http/httptest/server.go:198 +0x5e
  net/http.serverHandler.ServeHTTP()
      /usr/lib/golang/src/pkg/net/http/server.go:1597 +0x1ca
  net/http.(*conn).serve()
      /usr/lib/golang/src/pkg/net/http/server.go:1167 +0xc00
```

[test]