Numerous improvements

• The role no longer attempts to install the unzip binary locally onto
  the Ansible control host; it is now a hard dependency and role execution
  will fail if unzip is not in the PATH on the control host.
• Snapshot agent installation and configuration (thanks @drewmullen)
• Delegate Consul datacenter DNS domain to Consul (thanks @teralype)
• Allow DNSmasq binding to particular interfaces (thanks @teralype)
• Update local tasks (thanks @sgrimm-sg)
• Update documentation