Fix config stanza reading login in the splunkenv.py

[echipachenko]

Method get_conf_stanzas internally calls
$SPLUNK_HOME/bin/splunk cmd btool server list
This command leads to accumulated output. It reads server.conf files from all apps.
Such behaviour may lead to invalid results, if an app has different (not supported) format in the conf file.

I suggest to change login and read configs only from the system app:
$SPLUNK_HOME/bin/splunk cmd btool server list --app=system

[hetangmodi-crest]

Given the use case and fix, a rather non-breaking fix would be allowing developers to pass their custom scope when getting certain conf file details rather than hard-coding it to system. The default stays as is, and developers can have an option to pass the scope (the value for the --app parameter.