VLOG instead of failure::log for fbtrace
VLOG instead of failure::log for fbtrace

Summary: On some hosts this happens very often and spews the log.

Test Plan: tests

Reviewed By: @pavlo-fb

Differential Revision: D1859731
synecdoche/mcrouter,zhlong73/mcrouter,easyfmxu/mcrouter,yqzhang/mcrouter,synecdoche/mcrouter,synecdoche/mcrouter,evertrue/mcrouter,seem-sky/mcrouter,glensc/mcrouter,zhlong73/mcrouter,apinski-cavium/mcrouter,yqzhang/mcrouter,tempbottle/mcrouter,nvaller/mcrouter,seem-sky/mcrouter,is00hcw/mcrouter,glensc/mcrouter,evertrue/mcrouter,nvaller/mcrouter,easyfmxu/mcrouter,leitao/mcrouter,evertrue/mcrouter,nvaller/mcrouter,is00hcw/mcrouter,apinski-cavium/mcrouter,yqzhang/mcrouter,evertrue/mcrouter,reddit/mcrouter,tempbottle/mcrouter,tempbottle/mcrouter,easyfmxu/mcrouter,reddit/mcrouter,zhlong73/mcrouter,leitao/mcrouter,yqzhang/mcrouter,zhlong73/mcrouter,leitao/mcrouter,apinski-cavium/mcrouter,apinski-cavium/mcrouter,facebook/mcrouter,easyfmxu/mcrouter,reddit/mcrouter,facebook/mcrouter,tempbottle/mcrouter,facebook/mcrouter,is00hcw/mcrouter,synecdoche/mcrouter,seem-sky/mcrouter,glensc/mcrouter,facebook/mcrouter,reddit/mcrouter,nvaller/mcrouter,is00hcw/mcrouter,leitao/mcrouter,seem-sky/mcrouter,glensc/mcrouter