Integration testing against ScyllaDB too (currently only Cassandra is tested)

Problem

When we replaced Cassandra's CCM with scylla-ccm, we forgot to add necessary --scylla command line parameter. As a result, tests have been always run against Cassandra, not ScyllaDB.

Intended outcome

We want to run integration tests both against ScyllaDB and Cassandra.

Suggested solution

Run integration tests twice:

1. First with default settings - against Cassandra;
2. Then with custom env params - against ScyllaDB. The test framework already accepts such params.