Separate stream flushing and file syncing in file-audit-endpoint

file-audit-endpoint currently provides synchronized attribute, which allows to set whether should be output stream flushed and file descriptor synced after writing every audit log message. To have it enabled entail big performance drop, while have it disabled provides minimal data safety. Should be possible to use compromise - as in legacy audit log, to flush stream only.

More fine-tuned settings will be possible if the two can be set separately - standalone atttribute for stream flushing (autoflush for example) and for file descriptor syncing (synchronized for example).

Subsystem parsing and transformer tests will be added.