TChannelRequest: factor out #shouldRetryError
TChannelRequest: factor out #shouldRetryError

vanloswang/tchannel,vanloswang/tchannel,RyanTech/tchannel,Zirpon/tchannel,bunnyblue/tchannel,Zirpon/tchannel,bunnyblue/tchannel,chenwenbin928/tchannel,chenwenbin928/tchannel,i/tchannel,hustxiaoc/tchannel,savaki/tchannel,savaki/tchannel,RyanTech/tchannel,bunnyblue/tchannel,i/tchannel,sasa233/tchannel,vanloswang/tchannel,benfleis/tchannel,RyanTech/tchannel,hustxiaoc/tchannel,i/tchannel,hustxiaoc/tchannel,savaki/tchannel,benfleis/tchannel,sasa233/tchannel,sasa233/tchannel,chenwenbin928/tchannel,Zirpon/tchannel,benfleis/tchannel