* Support resource-based bootstrapping for backend.
Outside of static configuration, most of the persistent state of an
auth server exists as a collection of resources, stored in its
backend. The resource API also forms the basis of Teleport's more
advanced dynamic configuration options.
This commit extends the usefulness of the resource API by adding
the ability to bootstrap backend state with a set of previously
exported resources. This allows the resource API to serve as a
rudimentary backup/migration tool.
Notes: This features is a work in progress, and very easy to misuse;
while it will prevent you from overwriting the state of an existing
auth server, it won't stop you from bootstrapping into a wildly
misconfigured state. In general, resource-based bootstrapping is
not a complete solution for backup or migration.
* update e-ref
Moved expiry field from spec to metadata for services.Users and updated
expiry check to prefer metadata and fallback to spec if not found. Added
test coverage.
Forrest Marshall