Add pool reuse test to unit tests
Add pool reuse test to unit tests

Add a test to confirm that the pool allocator will iterate through all
the pools even if some earlier ones were freed before coming back to
previously allocated pools.

Signed-off-by: Chris Telfer <9cf1a5ba8f085fe3bf87fd3e4704febafc338899@docker.com>

medallia/libnetwork,abhi/libnetwork,abhi/libnetwork,docker/libnetwork,vdemeester/libnetwork,vdemeester/libnetwork,mahak/libnetwork,vdemeester/libnetwork,medallia/libnetwork,abhi/libnetwork,docker/libnetwork,mahak/libnetwork,mahak/libnetwork,docker/libnetwork,medallia/libnetwork