gqltest: split tests so that every test case is run against the clean database
Created by: sashaostrikov
Previously every test case was run in the same test function which led to every consequent test case use the database with some state changed from every previous test case. As all the test cases deal with similar tables in the database, this can lead to unexpected behaviour or false positives, which possibility is now eliminated as every test runs against the clean database.
Test plan
Existing tests should pass