Bug in logic of parser rsyslog_conf.py

[wushiqinlou]

Before RHEL8, the format of rsyslog.conf is like:

$IncludeConfig /etc/rsyslog.d/*.conf
$ModLoad imtcp

However, it changes like following in RHEL8:

include(file="/etc/rsyslog.d/*.conf" mode="optional")
module(load="imuxsock" 
       SysSock.Use="off")

We also need to consider the RainerScript when parsing rsyslog.conf, however, current parser rsyslog_conf can not handle such situation. Per our discussion in https://github.com/RedHatInsights/insights-core/pull/1952, we decide to return the content directly with format line by line. As it is necessary to refactor the return value, this issue is raised to remove self.config_items and def config_val