Correct metadata ordering issue in tests

Some test including test_volume_get_all_filters
fails randomly because metadata is in a dict and
the items order is undefined.
The test comparison was changed to avoid unexpected
test results.

Change-Id: Ibb24d21cd05aa1eefb45b61c63de067b34fb1013
Closes-Bug: #1293792
Merge "Correct metadata ordering issue in tests"