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

More speedups
Prune children searches
Merge pull request #48 from sloppyfocus/prune_search_children

Prune children searches
Merge pull request #39 from thekad/base_types

Resource managers dont't overload type
Speed up attrs(merge_container_attrs=True) calls

This change speeds up calls to attrs which merge container attributes by
performing a single sql query for each generation of parents instead of
performing a sql query per parent.
Merge pull request #49 from sloppyfocus/speedup_merge_container_attributes

Speed up attrs(merge_container_attrs=True) calls
This should fix the error down below

The problem is that I forgot to actually get the object, so the pool is
a string, not a real clusto object. Once I ``get_by_name()`` it we can
manipulate it as I intended to.
PEP8 fixes
Merge pull request #51 from thekad/fix-deallocate

This should fix the error down below
Merge branch 'master' into strict_get_from_pools

Conflicts:
	src/clusto/test/drivers/categories/pooltests.py
Merge pull request #38 from thekad/strict_get_from_pools

Strict get from pools