Include the primary bootloader and ramdisk in the BOOT/

This will copy over the primary bootloader (if it exists and defined)
over to the zip_root/BOOT.

This is required by encore as we need to make sure we have the correct
primary bootloader to go with the kernel.

Change-Id: I3fef417011b9c7a63109d10fc8e6794e58f73c31
Require signapk.jar for Flakeflash images

Build signapk.jar which is required to sign the recovery flakeflash image.

Change-Id: I6db422199c8afd3a3f43919980d0893f8d3efc6e
remove unused BOARD_USES_COMBINED_RECOVERY

Change-Id: I79520c510488d63d469b0d1a3a099420f7de1fe6