HA mailbox, build configuration

[spoon16]

This is the build configuration used by Zimbra/zm-docker#26. It build's zm-mailbox using the high availability (feature/ha) branch. That build is used to provision the HA reference environment in docker swarm.

[CLAassistant]

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✅ gordyt
❌ spoon16
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[cbacit]

It would be great if there was feature...