add debugging for when changes-sinces fails

this test fails about once a month, even in it's current format.
It's hard to tell why at this point, so put in enough debugging so
that the next failure will let us understand what's going on.

Change-Id: I95b91faeea70536f6f4d5226cf6ebda20b93412d
Merge "add debugging for when changes-sinces fails"