Replace CompletableFuture with Future fixing spurious test failures

12:46:48 INFO  MockOkapi            Waiting for 6000 ms before continuing
12:46:51 ERROR PatronHandler        Exception calling OKAPI
io.vertx.core.VertxException: Connection was closed
12:46:51 ERROR ?                    io.vertx.core.VertxException: Connection was closed
12:46:51 DEBUG Wire                  << "HTTP/1.1 500 Internal Server Error[\r][\n]"
12:46:51 DEBUG Wire                  << "content-type: application/json[\r][\n]"
12:46:51 DEBUG Wire                  << "content-length: 62[\r][\n]"
12:46:51 DEBUG Wire                  << "[\r][\n]"
12:46:51 DEBUG aultClientConnection Receiving response: HTTP/1.1 500 Internal Server Error

[ERROR]   MainVerticleTest.testPlaceItemHoldRequestTimeout:999 1 expectation failed.
Expected status code <408> but was <500>.