test_maple_tree: testing the cyclic allocation

This tests the interactions of the cyclic allocations, the maple state
index and last, and overflow.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://lore.kernel.org/r/170820144894.6328.13052830860966450674.stgit@91.116.238.104.host.secureserver.net


Signed-off-by: Christian Brauner <brauner@kernel.org>