handover test: add 'expect-ts-use' to clarify tests

In handover tests, it can be hard to follow which lchans are currently
occupied. The expect-ts-use command is like an assertion for a specific
distribution of used lchans, and helps understanding test intentions.

Change-Id: I6f4b573de7faace2d6bfe4f58b568e69c74dd07d
1 file changed