Defer realization of before and after tasks until flow creation
Use "vcpus" in flavors in setup

It was "vcpu" which isn't consistent with what Nova API returns.
Add event_id_key class variable to EventResource descendants

Allows to avoid simple overrides of event_id() method
Add __repr__ to UnboundTask
Make plugins work even w/o Collection around them

Also add caching of unbound tasks to make before= and after= work.
Flavor.create now works even with string instead of "swap"

Nova API returns empty string in this field.
Put setup and cleanup into one flow for each cloud
Fix type of NovaNetwork in events
Merge origin/refactor-reset into refactor-reset