Don't build cache by default. Use BOARD_GENERATE_CACHEIMAGE to control it.

Change-Id: I5cee499a47d8cc1785634c4fdda126c2c57bdf80
Partially revert 8263ad86d4684ededd26113387c8b5a18799a036
Leave Aaron's commit part as it was

Change-Id: Ic3e79f55711822c306ab5801e5db89d7d7016a8c
Merge remote-tracking branch 'PA-build/kitkat' into kitkat