Make Cassandra replication factor configurable (issue #787)

Add CASSANDRA_REPLICATION_FACTOR environment variable and
--cassandra-replication-factor CLI argument to cassandra_config.py.

Update all four table store constructors (ConfigTableStore,
KnowledgeTableStore, LibraryTableStore, IamTableStore) to accept
an optional replication_factor parameter and use it in keyspace
creation CQL queries.

Thread the replication factor through all service constructors:
Configuration, KnowledgeManager, Librarian, IamService, and
knowledge store Processor.

trustgraph-flow/trustgraph/tables/library.py

@@ -40,9 +40,11 @@ class LibraryTableStore:
     def __init__(
             self,
             cassandra_host, cassandra_username, cassandra_password, keyspace,
+            replication_factor=1,
     ):
 
         self.keyspace = keyspace
+        self.replication_factor = replication_factor
 
         logger.info("Connecting to Cassandra...")
 
@@ -77,12 +79,11 @@ class LibraryTableStore:
 
         logger.debug("Keyspace...")
 
-        # FIXME: Replication factor should be configurable
         self.cassandra.execute(f"""
             create keyspace if not exists {self.keyspace}
                 with replication = {{
                    'class' : 'SimpleStrategy',
-                   'replication_factor' : 1
+                   'replication_factor' : {self.replication_factor}
                 }};
         """);