Pack file_contexts into target_files zip.

file_contexts (specified by SELINUX_FC) is needed both when building
and (re)packaging. We used to use the copy in out/ when building, and
looked for the copy in BOOT/RAMDISK/ when packaging from target_files
zip. With system_root_image enabled, the file_contexts needed for
building and packaging might be different from the one on device. So
we explicitly pack the file as META/file_contexts in target_files zip.

Also refactor out the overriding of selinux_fc property into
common.LoadInfoDict().

Change-Id: I94f9ea6671b3792c12c1c21573840743d63da39a
(cherry picked from commit aa7318c3849095aeb3bea00efbf303c0c40a089d)
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index a87363b..8fe4864 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -582,6 +582,8 @@
   if HasVendorPartition(input_zip):
     system_progress -= 0.1
 
+  # Place a copy of file_contexts into the OTA package which will be used by
+  # the recovery program.
   if "selinux_fc" in OPTIONS.info_dict:
     WritePolicyConfig(OPTIONS.info_dict["selinux_fc"], output_zip)
 
@@ -1538,15 +1540,7 @@
   OPTIONS.input_tmp, input_zip = common.UnzipTemp(args[0])
 
   OPTIONS.target_tmp = OPTIONS.input_tmp
-  OPTIONS.info_dict = common.LoadInfoDict(input_zip)
-
-  # If this image was originally labelled with SELinux contexts, make sure we
-  # also apply the labels in our new image. During building, the "file_contexts"
-  # is in the out/ directory tree, but for repacking from target-files.zip it's
-  # in the root directory of the ramdisk.
-  if "selinux_fc" in OPTIONS.info_dict:
-    OPTIONS.info_dict["selinux_fc"] = os.path.join(
-        OPTIONS.input_tmp, "BOOT", "RAMDISK", "file_contexts")
+  OPTIONS.info_dict = common.LoadInfoDict(input_zip, OPTIONS.target_tmp)
 
   if OPTIONS.verbose:
     print "--- target info ---"
@@ -1596,10 +1590,8 @@
       OPTIONS.source_tmp, source_zip = common.UnzipTemp(
           OPTIONS.incremental_source)
       OPTIONS.target_info_dict = OPTIONS.info_dict
-      OPTIONS.source_info_dict = common.LoadInfoDict(source_zip)
-      if "selinux_fc" in OPTIONS.source_info_dict:
-        OPTIONS.source_info_dict["selinux_fc"] = os.path.join(
-            OPTIONS.source_tmp, "BOOT", "RAMDISK", "file_contexts")
+      OPTIONS.source_info_dict = common.LoadInfoDict(source_zip,
+                                                     OPTIONS.source_tmp)
       if OPTIONS.package_key is None:
         OPTIONS.package_key = OPTIONS.source_info_dict.get(
             "default_system_dev_certificate",