Support /product partition

This CL will support the followings.
- installing a RRO package for framework from /product/overlay
- installing apps from /product/app
- installing priv-apps from /product/priv-app
- installing permissions from
  /product/etc/[default-permissions|permissions|sysconfig]

Bug: 64195575
Test: `mm` under frameworks/base/tests/[libs|privapp]-permissions
adb sync && adb reboot
adb shell cmd package list libraries
  => confirmed com.android.test.libs.product library
adb shell cmd package dump \
  com.android.framework.permission.privapp.tests.product
  => confirmed that the package is a priv-app

And I moved vendor/overlay/framework-res__auto_generated_rro.apk into
system/product/overlay/ on sailfish, and I confirmed that the RRO was
installed properly.

Change-Id: I16175933cebd9ec665d190cc5d564b5414a91827