Generate extra userdata partition if needed

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

Change-Id: I74c32d8316f0450a1445fe95a95e5cabb7a9dd1b
(cherry picked from commit ab46c15806af94b4eb8b738db91e933abfb088e3)
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
(cherry picked from commit 5c84893be3a81be5f67af3cef3190798c61cc1c5)

Conflicts:
	tools/releasetools/ota_from_target_files