ssl/dtls: add support for Raw Public keys

Instead of X.509 certificates now also Raw public keys are supported
and shown correctly.

This is described in this draft:
https://tools.ietf.org/html/draft-ietf-tls-oob-pubkey-11

Change-Id: Ibe7610aace31a19791b02e71ccd8d9ceb8cf979d
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Reviewed-on: https://code.wireshark.org/review/1372
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
(cherry picked from commit a8e6d128ab85da609915b92f3d9e370203b67131)
Reviewed-on: https://code.wireshark.org/review/2999
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Evan Huus <eapache@gmail.com>
ssl: move Certificate handshake dissection to ssl-utils

There are no dissection differences between DTLS and SSL, so move to
ssl-utils. While at it, skip dissection when the tree is NULL, remove
the plural from certificates length (the length is always larger than
ome), fix type of "ti" for dtls, get rid of "failsafe" subtree
assignment in ssl, get rid of tvb_ensure_bytes_exist in ssl.

Unrelated changes: fix param (tvb vs sub_tvb) for DTLS KeyExchange
handshake messages.

Change-Id: Iecaa45a7a601e55a52aa16180cf219a122fbe95a
Reviewed-on: https://code.wireshark.org/review/2985
Reviewed-by: Anders Broman <a.broman58@gmail.com>
(cherry picked from commit ba6d2e7cc8d8d06e9b879813d3e11dc7855a9e99)
Reviewed-on: https://code.wireshark.org/review/3000
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Hauke Mehrtens <hauke@hauke-m.de>
Reviewed-by: Evan Huus <eapache@gmail.com>