configure progress bar during block OTA script generation

Emit script commands to produce a more accurate progress bar (for full
block OTAs) and a working progress bar (for incremental block OTAs) --
ones that are driven by the progress callback from the thing actually
writing the system image.

Change-Id: Ifca10be68cfdaab7135d23515bd0ae5be2f98a16
1 file changed