adb: replace reboot service with exec of /system/bin/reboot.

Test: adb reboot
Test: adb reboot fastboot
Change-Id: Ia4146dde7ef3ae00a782dbe68aff166d63eabdb9
diff --git a/reboot/Android.bp b/reboot/Android.bp
index 805fd9a..cc71723 100644
--- a/reboot/Android.bp
+++ b/reboot/Android.bp
@@ -5,4 +5,5 @@
     srcs: ["reboot.c"],
     shared_libs: ["libcutils"],
     cflags: ["-Werror"],
+    recovery_available: true,
 }