add bootloader restrictions to OTA metadata

Doesn't touch device code.

Change-Id: I8941e5a07dc589514446544a15f17f623101ecca
diff --git a/releasetools.py b/releasetools.py
index 952d9ff..d8c3361 100644
--- a/releasetools.py
+++ b/releasetools.py
@@ -34,6 +34,7 @@
     bootloaders = m.group(1).split("|")
     if "*" not in bootloaders:
       info.script.AssertSomeBootloader(*bootloaders)
+    info.metadata["pre-bootloader"] = m.group(1)
 
 
 def InstallRadio(radio_img, api_version, input_zip, info):