sign_target_files_apks: fix recovery patch generation

When rebuilding recovery, the boot images created for patching
purposes still were being signed with the old verity key and
not the new one specified on the command line.

In addition, the replacement verity public key in the boot ramdisk
wasn't being used.

Change-Id: I451e17d1cf08c507580c4b58134c1069532740e8
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>