Read in bytes to fix --reuse-key on Python 3 (#6069)
Read in bytes to fix --reuse-key on Python 3 (#6069)

* Read bytes for now for compatibility

* add clarifying comment

letsencrypt/letsencrypt,lmcro/letsencrypt,letsencrypt/letsencrypt,lmcro/letsencrypt,stweil/letsencrypt,stweil/letsencrypt