Make RollingFile filePattern an absolute path

[mayrstefan]

What does this PR change?

Should fix #5883. Log4J2 should no more try to write the rotated logfile into CATALINA_HOME

GUI diff

No difference.

Documentation

• No documentation needed: only internal and user invisible changes

Test coverage

• No tests: no functional change

Links

Fixes #5883

• [x] DONE

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