Refactor generic cleanup mechanism part 3

Current cleanup mechanism is awful. It's hardcoded, without repeat on failures,
contains a lot of mistakes, in some places it is too fast (in case of deletion of VMs)
in other to slow (like deletion of users). As well there is mix of cleanup mechanism
and resource cleanup mechanism.
To resolve these all issues this patch introcude a cleanup engine that resolves all issues
above.
It's resource based, so to add new resouce you should just a make subclass of base.Resource
and probably override some of methods like (list, delete, is_deleted) and that's all.
All complexity of managing:
0) waiting until async deletion is finished
1) repeat on failure logic
2) greaceful failure handling
3) parallelization
4) plugin support
Is hidden deep inside cleanup engine
+ bonus we are able to specify now single resource (without clenaping whole service)

PART 3:
-------

*) Refactor all contexts cleanups method to use new generic cleanup engine
   insted of cleanup.utils
*) Remove obsolate cleanup.utils
*) Fix all tests

bp benchmark-context-cleanup-refactor

Change-Id: I70557e6ebb56bbe565792d9ee854d3e78428a881
Merge "Refactor generic cleanup mechanism part 3"