fix: logging configuration properties not working from launcher.cnl

[ttugrul]

Motivation
Logging properties set in launcher.cnl (like var cloudnet.log.level OFF) were being ignored.

Modification
Changed logback XML files to read system properties directly instead of using cached variables:
${cloudnet.log.level} → ${cloudnet.log.level:-DEBUG}
${cloudnet.log.path} → ${cloudnet.log.path:-local/logs}

Result
Logging configuration from launcher.cnl now works correctly. Users can set custom log levels and paths.

Other context
Fixes timing issue where logback initialized before system properties were available.

[derklaro]

I wonder if it would be better to move the variable subsitutation into the variable values, so that they are defined at the top of the configuration. I think the same result can be achived using something like:

<variable name="cloudnet.log.level" value="${cloudnet.log.level:-DEBUG}"/>

[derklaro]

@ttugrul thanks!