KAFKA-1373; Set first dirty (uncompacted) offset to first offset of the
log if no checkpoint exists. Reviewed by Timothy Chen and Neha Narkhede.
KAFKA-1323; Fix regression due to KAFKA-1315 (support for relative
    directories in log.dirs property broke). Patched by Timothy Chen and
    Guozhang Wang; reviewed by Joel Koshy, Neha Narkhede and Jun Rao.
KAFKA-1356 Topic metadata requests takes too long to process; reviewed by Joel Koshy, Neha Narkhede, Jun Rao and Guozhang Wang