releasetools: Update the path to /default.prop for A/B devices.

On A/B devices (i.e. system_root_image="true"), /default.prop is
packaged at ROOT/default.prop (as opposed to BOOT/RAMDISK/default.prop
for non-A/B devices). Update the path so that we handle properties like
ro.bootimage.build.fingerprint properly.

The one for recovery is not affected, which stays at
BOOT/RAMDISK/default.prop for A/B devices and gets updated correctly.

Bug: 30811237
Test: Verify the property in the generated signed-TF.zip.
Change-Id: Id201a042d7ea988a64f89c6d04f43326a9851e27
(cherry picked from commit 28e2fa1726f3434417e2f0d5f1a810cbd657a5e3)
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index b11225c..e646b96 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -232,11 +232,13 @@
     elif info.filename in ("SYSTEM/build.prop",
                            "VENDOR/build.prop",
                            "BOOT/RAMDISK/default.prop",
+                           "ROOT/default.prop",
                            "RECOVERY/RAMDISK/default.prop"):
       print "rewriting %s:" % (info.filename,)
       new_data = RewriteProps(data, misc_info)
       common.ZipWriteStr(output_tf_zip, out_info, new_data)
       if info.filename in ("BOOT/RAMDISK/default.prop",
+                           "ROOT/default.prop",
                            "RECOVERY/RAMDISK/default.prop"):
         write_to_temp(info.filename, info.external_attr, new_data)