[core] Fix recorder/logger initialization timing issue.

The HdrHistogramReader makes some problematic assumptions on the roles
played by start time, base time and histogram start/end times. This is
to be revisited in a future release of HdrHistogram (see
https://github.com/HdrHistogram/HdrHistogram/issues/69). In the meantime
this change will make YCSB record as expected by the reader:
a. Set histogram log base time (same as start time)
b. Only create the recorder after the log has been setup