qa/mk.logfarm: improve resilience
qa/mk.logfarm: improve resilience

- src and dst may be the same filename, so don't pmlogmv
- skip timestamping if dst archive name does not look like a YYYYDDMM...
  format name
- skip pmlogrewrite if pmlogcheck fails (e.g. deliberately populating
  the pmlogger farm with a bad archive for testing)

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp