info: Fix HashMap ordering assumption in unit test

The unit test assumes a particular serialized form of the state tree
nodes, which isn't guaranteed when iterating over a HashMap. This causes
the unit tests to fail with some JDKs, in particular JDK 8.

Target: trunk
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: https://rb.dcache.org/r/7198/
(cherry picked from commit 14797ddac174e77e1aabf2a1873e5878d3d311f2)
Merge pull request #763 from gbehrmann/fix/2.8/rb7198

info: Fix HashMap ordering assumption in unit test