releasetools: replace verity keyid

Replace verity keyid with the keyid extracted from cert
passed through --replace_verity_keyid. The veritykeyid in the
BOOT/cmdline of input target files is replaced with keyid
extracted from --replace_verity_keyid and written to the
output target files.

BUG: 28384658
Change-Id: Ic683f36f543c4fcd94b6f95e40f01200fbf45ee1