An error (e.g a typo) in a custom tripleo-heat-templates environment
file could lead to an invalid match block in /etc/ssh/sshd_config.
SSH fails-safe and refuses all logins in this case.
This change validates the migration_ssh_localaddrs parameter is an
array of IP addresses and removes and duplicate entries.
Change-Id: Ibcf144d960fe52f0eab0d5015bd30cf7c1e37e25
Closes-Bug: #1688308