Improve error messages when a user's pcr selection is not available o…

…n (#182)

the TPM host.

go-tpm/adapter.go

@@ -143,7 +143,7 @@ func WithAkCertificateUri(uriString string) TpmAdapterOptions {
 	return func(tca *tpmAdapter) error {
 		// Azure vTPM does not require an AK certificate -- an empty string is allowed
 		if uriString == "" {
-			logrus.Warn("The ak_certificate configuration is not defined will not be included in TPM evidence.")
+			logrus.Warn("The ak_certificate was not defined in configuration and will not be included in TPM evidence.")
 			return nil
 		}
 

go-tpm/pcrs.go

@@ -21,7 +21,7 @@ func (tpm *trustedPlatformModule) GetPcrs(selection ...PcrSelection) ([]byte, er
 
 	_, pcrValues, err := tpm.ctx.PCRRead(pcrSelection, nil)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrapf(err, "Failed to read PCRs with selection %+v", pcrSelection)
 	}
 
 	selectionList, err := pcrValues.SelectionList()