temporarily trust the health manager

(disable faulty defensive logic against scaling down)
bundle update and cleanup various Sequel deprecations from upgrade [finishes #52240981]
Restart app even if last_updated field from HM is nil

[#52110279]
do a refresh in the spec
Randomize DEA selection a little more

[Finishes #51757383]
replaces Model.delete with Model.dataset.destroy in test
listen to new health manager request messages

reconciles health manager state assumption against desired state to
determine if health manager requests should be executed or ignored

new health manager messages include a subset of the known state that's
relevant to the request (versions, running counts)
correctly handle stop requests for multiple instances
actually handle health manager requests
correctly treat running info as having symbol keys
explicitly require sinatra/base
use new by-version instance hm stop requests
explicit subject is bad, mmkay
back-fill tests for RestController#enumerate
extract enumerate_dataset out of #enumerate
renamed ServiceInstance to ManagedServiceInstance
redirect GET /v2/managed_service_instances/:guid to /v2/service_instances/:guid
lift credentials up back to base class
start working on provided service instance model
lift part of validate up back to service instance