Report download metrics for android

Report the metrics with libmetricslogger.
Tron varz added:
ota_update_engine_attempt_current_bytes_downloaded_mib
ota_update_engine_successful_update_total_bytes_downloaded_mib
ota_update_engine_successful_update_download_overhead_percentage

Test: build on sailfish
Change-Id: I4350c2030223d265a138aa07d2720413a5686d5a