Currently if a pod is being scheduled with no meta.RolesKey label
attached to it, per convention the first configured mesos (framework)
role is being used.
This is quite limiting and also lets e2e tests fail. This commit
introduces a new configuration option "--mesos-default-pod-roles" defaulting to
"*" which defines the default pod roles in case the meta.RolesKey pod
label is missing.
- refactor queue.Pod construction to take functional options, privatize Pod fields
- refactor DelayFIFO and HistoricalFIFO to offer consistent, more useful Pop() funcs
- refactor pod update processing changes; long term we should somehow combine with the special pod config source that we are using for mirror pods
- task launch timer cleanup
