USN-6663-2: OpenSSL update

USN-6663-1 provided a security update for OpenSSL.
This update provides the corresponding update for
Ubuntu 16.04 LTS.

Original advisory details:

As a security improvement, this update prevents OpenSSL
from returning an error when detecting wrong padding
in PKCS#1 v1.5 RSA, to prevent its use in possible
Bleichenbacher timing attacks.

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