Allows shipping snapshots automatically to remote clusters on a cron,
identically to how autobackup handles local snapshot exports.
VMs are selected based on configured tags, and individual destination
clusters can be specified based on a colon-separated suffix to the
tag(s).
Automirror snapshots use the prefix "am" (analogous to "ab" for
autobackups) to differentiate them from normal "mr" mirrors.
Joshua M. Boniface
078d48a50b