Unit tests to verify relative_time were not calling the parse_time

function in query.cc as expected. Changing the way we post query
made the the function to be called properly. Also the UT has been
added to check OBJECT_VALUE_TABLE.
Code changes:
Query class has been moved from perftest.py to analytics_fixture.py
as it is used elsewhere and util would be a proper place.
Instead of query query_json objects are called so that passed parameters
are not interpreted by the util scripts before calling the actual functions.
Test:
Coverage report shows the parse_time function being referred in query.cc