Update memory configuration inheritance

* Use 'inherit-product' instead of 'inherit-product-if-exists'
  for the Dalvik heap config, and HWUI memory limits,
  so that the build fails if those files do not exist
* Device doesn't boot with the default values, it
  runs Out-of-memory because of improper configuration

Change-Id: I90f02a118f3791e482bbe49507256f5e2e7cc47a