append_conf: append parameters to db config

PR to introduce this parameter

conf: add a general way to append parameters to db config #373

Function

Append multiple parameters to scylla.yaml in node_setup() -> config_setup()

Specification

• the multiple scylla parameters are splited by "\n"
• the append_conf should be quoted by double quotation marks, the "\n" needs to be escaped
• use escape char when you want to use double quotation marks insider the parameters

Good Examples:

• append_conf: "\nenable_keyspace_column_family_metrics: true\nexperimental: true\n"
• append_conf: "audit: \"table\"\naudit-keyspaces: \"keyspace1\"\naudit-categories: \"ADMIN,AUTH,QUERY,DML,DDL,DCL\"\n"