jenkins: Force Full OTA (Don't generate incremental update)

Remove the last intermediate zip if FORCE_FULL_OTA is defined.
Sometimes, we need to generate full zip
For ex:
 - TLS changes
 - releasekey changes
 - Major version update
 - Corrupt of previous update

Change-Id: I6231993964d1263469e2f0ac3c2509c1b339564b