tests: fix test_compute to have predictable service list

The _create_service_entries() method in test_compute.py accepted
a dict for the list of services. The tests would then pull out
the first item in the list of keys of the dict. When the python
hash seed is set to a random value the list of keys has no
predictable ordering, causing the test suite to break. Changing
the data structure to use a list of lists instead of a dict
ensures strict ordering.

Related-bug: #1350287
Change-Id: I01a0d4cfb086eb94b49d25b65daf08e55e2087b4
Merge "tests: fix test_compute to have predictable service list"