test for ExclusivePool membership before inserting into another pool
get_from_pools() should *only* get from _pools_
Add a get_from_entities()

@synack points out correctly that it is actually useful to join pools
and, say, datacenters. Or pools and servers that contain more servers
(theoretically a hypervisor). So I am renaming get_from_pools() to
get_from_entities(), which is capable of lax joining entities, and I am
creating a simple get_from_pools() that is strict about the type being
passed to get_from_entities()
Resource managers dont't overload type

The _clusto_driver attribute is already unique per driver, while
_clusto_type should be more generic. In this case all resource managers
share the same _clusto_type except for the IP Manager, but I think that
shouldn't be the case.
Filter by pool
Speed up contents lookup
Turn off debugging
Fix bad in_ clause
Remove content_attrs filter for pool
Remove trailing whitespace
Remove more trailing whitespace
Modify contents() to batch up 500 rows at a time
Add tests for clusto.util
Fixed a bug due to bad linting
Change ValueError to AssertionError
Merge pull request #46 from sloppyfocus/speed_up_stuff

Speed up stuff
Abstract _get_contents into a separate method
Fix linting errors
Add grandchildren contents() test
Merge pull request #47 from sloppyfocus/more_speedups

More speedups