ota: Generate recovery-from-boot.p file

This may be wanted to update the recovery with system updates

Change-Id: Iacd41be7a8018cbc08b2606485d446756910f506
ota: Allow devices to skip generation of recovery-from-boot.p

* Not all devices have a real recovery partition, so those devices
  should skip this generation step.

Change-Id: I4abc3f92b879e6997e4874543ec9772c3179b1d0
Fixed building incrementals when "no separate recovery" is specified.

Change-Id: I1d7add44554ebc4b68dc09debdd0c0fb229061a9
Generate extra userdata partition if needed

* To support variants of devices which may come in 16/32/64GB variants.

Change-Id: I74c32d8316f0450a1445fe95a95e5cabb7a9dd1b