releasetools: Fix the missing 'post-build' in full OTAs.

The line was unintentionally removed in commit 7f804ba.

Test: ota_from_target_files.py generates a full OTA. Check the package
      metadata.

Change-Id: Icae88e2a9bb2bfc450a3d0d7ab524d6a6eac9df5
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 7e970a9..8222377 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -331,6 +331,7 @@
   target_fp = CalculateFingerprint(oem_props, oem_dicts and oem_dicts[0],
                                    OPTIONS.info_dict)
   metadata = {
+      "post-build": target_fp,
       "pre-device": GetOemProperty("ro.product.device", oem_props,
                                    oem_dicts and oem_dicts[0],
                                    OPTIONS.info_dict),