server: refine time query (#2506)
server: refine time query (#2506)

Log slow query even if there is error.
Reduce slow time from 1s to 300ms.
JinheLin/tidb,ngaut/tidb,EvilMcJerkface/tidb,qiuyesuifeng/tidb,anywhy/tidb,ueizhou/tidb,c4pt0r/tidb,mccxj/tidb,qiuyesuifeng/tidb,ngaut/tidb,Cofyc/tidb,ngaut/tidb,EvilMcJerkface/tidb,louishust/tidb,simon-xia/tidb,pingcap/tidb,spongedu/tidb,tiancaiamao/tidb,c4pt0r/tidb,silentred/tidb,ming-relax/tidb,kyle-wang/tidb,yuanwhy/tidb,c4pt0r/tidb,Nify/tidb,astaxie/tidb,pingcap/tidb,zs634134578/tidb,coocood/tidb,c4pt0r/tidb,liyu4/tidb,cosmtrek/tidb,Cofyc/tidb,c4pt0r/tidb,ngaut/tidb,simon-xia/tidb,liyu4/tidb,yangwenmai/tidb,myrice/tidb,kyle-wang/tidb,c4pt0r/tidb,JinheLin/tidb,myrice/tidb,qhsong/tidb,anywhy/tidb,CodeRushing/tidb,XuHuaiyu/tidb,kyle-wang/tidb,silenceper/tidb,coocood/tidb,gaocegege/tidb,8cbx/tidb,zs634134578/tidb,wusphinx/tidb,ngaut/tidb,louishust/tidb,8cbx/tidb,ming-relax/tidb,kyle-wang/tidb,zimulala/tidb,qhsong/tidb,zimulala/tidb,ueizhou/tidb,kyle-wang/tidb,yangwenmai/tidb,spongedu/tidb,kyle-wang/tidb,Nify/tidb,XuHuaiyu/tidb,gaocegege/tidb,ngaut/tidb,silentred/tidb,pingcap/tidb,astaxie/tidb,yuanwhy/tidb,pingcap/tidb,pingcap/tidb,tiancaiamao/tidb,mccxj/tidb,wusphinx/tidb,cosmtrek/tidb,andelf/tidb,CodeRushing/tidb,pingcap/tidb,silenceper/tidb,andelf/tidb