main: update schema lease argument to duration format. (#1864)
main: update schema lease argument to duration format. (#1864)

Allows use to use a lease duration less than a second.
XuHuaiyu/tidb,anywhy/tidb,pingcap/tidb,liyu4/tidb,c4pt0r/tidb,ngaut/tidb,qhsong/tidb,kyle-wang/tidb,silentred/tidb,kyle-wang/tidb,ueizhou/tidb,qiuyesuifeng/tidb,ngaut/tidb,liyu4/tidb,kyle-wang/tidb,kyle-wang/tidb,ngaut/tidb,louishust/tidb,tiancaiamao/tidb,ngaut/tidb,cosmtrek/tidb,Nify/tidb,pingcap/tidb,coocood/tidb,Cofyc/tidb,andelf/tidb,mccxj/tidb,8cbx/tidb,c4pt0r/tidb,silenceper/tidb,Nify/tidb,myrice/tidb,mccxj/tidb,c4pt0r/tidb,ueizhou/tidb,EvilMcJerkface/tidb,zs634134578/tidb,yuanwhy/tidb,XuHuaiyu/tidb,CodeRushing/tidb,kyle-wang/tidb,c4pt0r/tidb,simon-xia/tidb,8cbx/tidb,tiancaiamao/tidb,pingcap/tidb,louishust/tidb,kyle-wang/tidb,spongedu/tidb,wusphinx/tidb,astaxie/tidb,yuanwhy/tidb,ming-relax/tidb,simon-xia/tidb,wusphinx/tidb,JinheLin/tidb,astaxie/tidb,c4pt0r/tidb,c4pt0r/tidb,zimulala/tidb,Cofyc/tidb,JinheLin/tidb,pingcap/tidb,spongedu/tidb,cosmtrek/tidb,coocood/tidb,ming-relax/tidb,andelf/tidb,gaocegege/tidb,zs634134578/tidb,CodeRushing/tidb,qhsong/tidb,myrice/tidb,qiuyesuifeng/tidb,yangwenmai/tidb,ngaut/tidb,silentred/tidb,gaocegege/tidb,silenceper/tidb,EvilMcJerkface/tidb,pingcap/tidb,anywhy/tidb,pingcap/tidb,zimulala/tidb,yangwenmai/tidb,ngaut/tidb