Fix ossec rules_exclude and add support for multiple files in exclude

[jzelina]

• fix the parameter to configure rule exclusion in manager
  (rule_exclude had not been used, ossec_ruleset_rule_exclude was not fully implemented)
• add configuration support for multiple rules exclusion files
  e.g. ossec_ruleset_rule_exclude => ['0215-policy_rules.xml', '0020-syslog_rules.xml'],
• remove rule exclusion code from agent, as according to documentation ossec ruleset is only supported by manager.
  agent did not include any ruleset fragments or templates