CDI support can fail due to Set.toString() used as Map key

Current CDI support sometimes fails, because it stores CassandraOperation instances in a map with String key representing a set of Qualifiers:

cassandraOperationsMap.put(bean.getQualifiers().toString(), ((Bean<CassandraOperations>) bean));

However, Set doesn't define iteration order (or even String representation for that matter), so with 2+ Qualifiers there's a good chance to get them in the wrong order and fail to find operations:

Bean<CassandraOperations> cassandraOperationsBean = this.cassandraOperationsMap.get(qualifiers.toString());

Example:
[@javax.enterprise.inject.Default(), @javax.enterprise.inject.Any()]
!=
[@javax.enterprise.inject.Any(), @javax.enterprise.inject.Default()]