BugLink: http://bugs.launchpad.net/bugs/1670508

In order to allow encryption on SMB connection we need to exchange
a session key and generate encryption and decryption keys.
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
(cherry picked from commit cabfb368)
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>