The parameter 'log_min_duration_statement' was updated to support unit
suffixes like 'ms' in [1], but reverted in [2] by accident.
[1] https://review.openstack.org/#/c/370982/
[2] https://review.openstack.org/#/c/537665/
Change-Id: I6fa6785bc8438ccc28a815abd1a99526ff03b87c
Signed-off-by: Zhao Chao <zhaochao1984@gmail.com>