Never close the socket while there are outstanding txns
Never close the socket while there are outstanding txns

Summary:
When HTTPTransaction is destroyed it invokes the handler's detachTransaction method.  The transaction has access to some socket structures which need to be valid in case the handler is using them.  The code that invoked closeWithReset() was not taking into account that some transactions may still be on the current call-stack, with CallbackGuards holding them open.  As the stack unwinds, the last txn will detach itself and the socket will cleanup in checkForShutdown.

Test Plan: Unit tests, will canary and canary with ASAN

Reviewed By: viswanath@fb.com

Subscribers: doug, bmatheny

FB internal diff: D1751679

Tasks: 5865651

Signature: t1:1751679:1419055313:af5b6f87baba89d900e1c64062aa36c0247b34ac

jgli/proxygen,hongliangzhao/proxygen,KublaikhanGeek/proxygen,Werror/proxygen,supriyantomaftuh/proxygen,jgli/proxygen,hiproz/proxygen,hongliangzhao/proxygen,chenmoshushi/proxygen,hongliangzhao/proxygen,wrmsr/proxygen,fqihangf/proxygen,chjp2046/proxygen,sssemil/proxygen,zhiweicai/proxygen,songfj/proxygen,Orvid/proxygen,chenmoshushi/proxygen,KublaikhanGeek/proxygen,LilMeyer/proxygen,luxuan/proxygen,sssemil/proxygen,raphaelamorim/proxygen,LilMeyer/proxygen,zhiweicai/proxygen,KublaikhanGeek/proxygen,pueril/proxygen,zhiweicai/proxygen,chjp2046/proxygen,fqihangf/proxygen,Werror/proxygen,jgli/proxygen,chjp2046/proxygen,hnutank163/proxygen,hnutank163/proxygen,zhenglaizhang/proxygen,zhiweicai/proxygen,chenmoshushi/proxygen,supriyantomaftuh/proxygen,fqihangf/proxygen,seem-sky/proxygen,hnutank163/proxygen,songfj/proxygen,hiproz/proxygen,chenmoshushi/proxygen,pueril/proxygen,seem-sky/proxygen,hiproz/proxygen,hiproz/proxygen,luxuan/proxygen,pueril/proxygen,sssemil/proxygen,seem-sky/proxygen,supriyantomaftuh/proxygen,songfj/proxygen,LilMeyer/proxygen,KublaikhanGeek/proxygen,luxuan/proxygen,hongliangzhao/proxygen,raphaelamorim/proxygen,zhenglaizhang/proxygen,seem-sky/proxygen,Werror/proxygen,Werror/proxygen,LilMeyer/proxygen,chjp2046/proxygen,Orvid/proxygen,sssemil/proxygen,zhenglaizhang/proxygen,pueril/proxygen,Orvid/proxygen,wrmsr/proxygen,wrmsr/proxygen,jgli/proxygen,songfj/proxygen,fqihangf/proxygen,wrmsr/proxygen,supriyantomaftuh/proxygen,raphaelamorim/proxygen,hnutank163/proxygen,zhenglaizhang/proxygen,Orvid/proxygen,raphaelamorim/proxygen