internal/task: convert reviewer names to emails for priv patch workflow

For golang/go#65756.

Change-Id: I4dac7da7e68bf545103b99bf7a2f09374397f986
Reviewed-on: https://go-review.googlesource.com/c/build/+/567055
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/internal/task/privx.go b/internal/task/privx.go
index fb1183c..95abf92 100644
--- a/internal/task/privx.go
+++ b/internal/task/privx.go
@@ -92,7 +92,11 @@
 		}
 		ctx.Printf("cherry-picked")
 		refspec := "HEAD:refs/for/master%l=Auto-Submit,l=Commit-Queue+1"
-		for _, reviewer := range reviewers {
+		reviewerEmails, err := coordinatorEmails(reviewers)
+		if err != nil {
+			return nil, err
+		}
+		for _, reviewer := range reviewerEmails {
 			refspec += ",r=" + reviewer
 		}