Consolidate the codes that handle reboot/shutdown.

Test: Choose `Reboot system now`, `Power off`, `Reboot to bootloader`
      from recovery UI respectively.
Test: `adb reboot recovery` while under sideload mode.
Change-Id: I0f3d55b80b472178ea4f6970b29cd9df0778b639
diff --git a/recovery.cpp b/recovery.cpp
index 5fc673e..42dad41 100644
--- a/recovery.cpp
+++ b/recovery.cpp
@@ -895,8 +895,8 @@
           // Print retry count on screen.
           ui->Print("Retry attempt %d\n", retry_count);
 
-          // Reboot and retry the update
-          if (!reboot("reboot,recovery")) {
+          // Reboot back into recovery to retry the update.
+          if (!Reboot("recovery")) {
             ui->Print("Reboot failed\n");
           } else {
             while (true) {