cmd/releasebot: allow final releases without an RC

Remove the requirement for a final release to have an RC, since
point releases may not have one.

Additionally adds some error logs when running ./make.bash

Change-Id: If52d19d01e9e2a49c16d9b55c782bd922637292b
Reviewed-on: https://go-review.googlesource.com/89037
Reviewed-by: Russ Cox <rsc@golang.org>

cmd/releasebot/git.go

@@ -302,15 +302,16 @@ func (w *Work) cherryPickCLs() {
 		if change != nil && labelValue(change, "TryBot-Result") >= +1 {
 			w.log.Printf("found trybot OK on Gerrit; skipping make.bash")
 		} else {
-			_, err = w.runErr("./make.bash")
+			b, err := w.runErr("./make.bash")
 			if err != nil {
 				w.logError(cl, fmt.Sprintf("make.bash after git cherry-pick failed:\n\n"+
 					"    git fetch origin %s\n"+
 					"    git checkout %s\n"+
 					"    git fetch origin %s\n"+
 					"    git cherry-pick %s\n"+
-					"    ./make.bash\n",
-					lastRef, lastCommit, cl.Ref, cl.Commit))
+					"    ./make.bash: %v\n",
+					lastRef, lastCommit, cl.Ref, cl.Commit, err))
+				w.log.Printf("./make.bash: %v: %s", err, b)
 				w.run("git", "reset", "--hard", "HEAD^")
 				continue
 			}

cmd/releasebot/main.go

@@ -515,7 +515,7 @@ func (w *Work) writeVersion() {
 	rc = fmt.Sprintf("rc%d", n)
 
 	if w.FinalRelease {
-		if !haveExisting {
+		if n-1 > 0 && !haveExisting {
 			w.logError(nil, fmt.Sprintf("cannot issue final release - code has changed since %src%d", version, n-1))
 			return
 		}