Two related features would help make arvados-dispatch-cloud play nicer with other ways instance tags are used in the same cloud account:

1. Admin can supply some tags that get set on all instances created by arvados-dispatch-cloud (e.g., {"myOrg-instance-class": "arvados", "admin-contact": "bob@example.com"})
2. Admin can control the tag prefix (currently a prefix is hard-coded by each driver, but this should be moved out to the dispatcher, and the driver should just do exactly what it's told)

Instance-specific resources (like NICs in Azure) should also be tagged, using the same tags as the instance.

Shared resources (like key pairs in EC2) should be tagged with the preconfigured tags, but not the per-instance tags. (Implementation: the driver doesn't know which tags are instance-specific, so the set of tags to use for shared resources should be supplied explicitly during driver initialization.)

Tag keys and values are case sensitive.