Allow devices to specify certain ro. props via TARGET_UNIFIED_DEVICE

This modifies buildinfo.sh to not set model, name, description, and
fingerprint in build.prop. These can then be set via custom init
lib.
This also fixes ota_from_target_files to function without these
props being preset.

Change-Id: Ia7dfcdea5aab7ebf51d3ab29a0d9e5751fc96663
build: allow mounting by partition name through edify

With more devices migrating over to emulated storage there is a need for
increased flexibility when mounting partitions. Edify scripts currently lack
the ability to mount emmc partitions by their labels, so busybox is used
as a reliable alternative.

This allows partitions to be mounted by name while still maintaining
compatibility with older recoveries.

To use define TARGET_SETS_FSTAB in the device's make files

Change-Id: I905740dd566f451b7ac48579a85e1b39a8cfd31a