Optimize drop-test memory usage

This patch makes sure drop-test uses the Collections.singletonList(),
so as to not waste memory on ArrayList, since we are only forwarding a
single entry.

Change-Id: Iaf4e7e408ed147177a40355b3c0ab2d4e18d133c
Signed-off-by: Robert Varga <robert.varga@pantheon.sk>