tests: Plumb dumps of the test trie into the gtest macros.

tests: Plumb dumps of the test trie into the gtest macros.

With this change, when one of the tests fails, it will output a dump
of the trie data structure, making it a little easier to tell what
happened.

Change-Id: I0816ed727ef0b50fefd7ec485356b4fe8790bfe1
Reviewed-on: https://gem5-review.googlesource.com/6267
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>