parse_baselines: add support for snapshot

The long running snapshot performance test has
a configuration structure a little bit different than
the other tests.

The  normal structure is:

baselines: {
        latency/throughput/cpu_utilization
                function
                        workload
}

The snap test did not do any difference between workload and
what what it would measure (latency, cpu utilization etc)i and
the workload field was missing from json. This made it incompatible
with the parse_baselines tool.

Signed-off-by: Diana Popa <[email protected]>

Author: dianpopa