KAFKA-20901: Enforce cordoned log directories configured with relative paths

[majialoong]

Kafka allows log.dirs to be configured with relative paths, but cordoned.log.dirs was validated and applied using the original configuration strings, whereas LogManager converts log directories to absolute paths and uses those paths for directory ID lookups.

As a result, configuring cordoned.log.dirs with the absolute path reported by DescribeLogDirs was rejected when log.dirs contained the equivalent relative path. Using the relative path passed validation, but it did not match the absolute path used internally, so the directory was not reported as cordoned to the controller.

This change consistently uses absolute paths when validating and applying cordoned.log.dirs, including during dynamic reconfiguration and broker heartbeat propagation.