Add ro.revision property to checkin headers

Early hardware revisions often have known issues.  Add the ro.revision
property to the header for the checkin reports so known issues can
be easily filtered.

Change-Id: I337b09ddfa41ebbe7f8f56223392b0bd491f897b

Author: colincross

services/java/com/android/server/BootReceiver.java

@@ -88,6 +88,8 @@ private void logBootEvents(Context ctx) throws IOException {
         final String headers = new StringBuilder(512)
             .append("Build: ").append(Build.FINGERPRINT).append("\n")
             .append("Hardware: ").append(Build.BOARD).append("\n")
+            .append("Revision: ")
+            .append(SystemProperties.get("ro.revision", "")).append("\n")
             .append("Bootloader: ").append(Build.BOOTLOADER).append("\n")
             .append("Radio: ").append(Build.RADIO).append("\n")
             .append("Kernel: ")