s4: add a minimal ktutil for selftest

s4: add a minimal ktutil for selftest

This minimalistic version of ktutil dumps all principal names and
encryption types from a keytab, eg:

./bin/samba4ktutil test.keytab
ktpassuser@HILLHOUSE.SITE (arcfour-hmac-md5)
ktpassuser@HILLHOUSE.SITE (aes256-cts-hmac-sha1-96)
ktpassuser@HILLHOUSE.SITE (aes128-cts-hmac-sha1-96)
ktpassuser@HILLHOUSE.SITE (des-cbc-md5)
ktpassuser@HILLHOUSE.SITE (des-cbc-crc)

This is all we need to run some tests against keytabs exported with
`samba-tool domain exportkeytab`.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>