src/pmlogger/pmlogger_check.sh: alternate strategy for finding primary logger's PID
src/pmlogger/pmlogger_check.sh: alternate strategy for finding primary logger's PID

If $PCP_RUN_DIR/pmlogger.pid does not exist, try symlink from
$PCP_TMP_DIR/pmlogger/primary -> <pid>.

Without this, qa/119 was sometimes failing ... not sure if this is
needed outside QA, but it cannot hurt, and it does further reduce
the chances of running more than one primary pmlogger (which is bad).

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