test.py: support arbitrary number of test suites
test.py: support arbitrary number of test suites

Scan entire test/ for folders that contain suite.yaml,
and load tests from these folders. Skip the rest.

Each folder with a suite.yaml is expected to have a valid
suite configuration in the yaml file.

A suite is a folder with test of the same type. E.g.
it can be a folder with unit tests, boost tests, or CQL
tests.

The harness will use suite.yaml to create an appropriate
suite test driver, to execute tests in different formats.

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla