Fix GCP metadata endpoint (#1350)

* Fix GCP metadata endpoint

This was broken a few months ago:

- c295133#diff-e3a5b197b3f4e8bc25ffcc06c8e810caL27
- c295133#diff-6cfb951705f6c4b248a6d3c6faa23069R27

```
bash-4.3# curl -H "Metadata-Flavor: Google" http://metadata.google.pkg/computeMetadata/v1/instance/id
curl: (6) Could not resolve host: metadata.google.pkg

bash-4.3# curl "http://metadata.google.internal/computeMetadata/v1/instance/id" -H "Metadata-Flavor: Google"
3395187815902811713
```

Internal case: `00012827`

* Add debug log when GCP host id gathering fails

Co-authored-by: Ben Keith <[email protected]>

pkg/core/hostid/gcp.go

@@ -5,6 +5,8 @@ import (
 	"io/ioutil"
 	"net/http"
 	"time"
+
+	"github.com/sirupsen/logrus"
 )
 
 // GoogleComputeID generates a unique id for the compute instance that the
@@ -24,7 +26,7 @@ func GoogleComputeID() string {
 }
 
 func getMetadata(path string) string {
-	url := fmt.Sprintf("http://metadata.google.pkg/computeMetadata/v1/%s", path)
+	url := fmt.Sprintf("http://metadata.google.internal/computeMetadata/v1/%s", path)
 	req, err := http.NewRequest("GET", url, nil)
 	if err != nil {
 		// This would only be due to a programming bug
@@ -39,6 +41,7 @@ func getMetadata(path string) string {
 
 	resp, err := c.Do(req)
 	if err != nil {
+		logrus.WithError(err).Debugf("Failed to query GCP Metadata endpoint at %s", url)
 		return ""
 	}
 	defer resp.Body.Close()