route53: re-use boto3 client in wait (#4724)
route53: re-use boto3 client in wait (#4724)

This change re-uses the boto3 client in the wait method of the route53
authenticator in order to make it more mockable for testing purposes.
letsencrypt/letsencrypt,lmcro/letsencrypt,lmcro/letsencrypt,letsencrypt/letsencrypt,jsha/letsencrypt,stweil/letsencrypt,jsha/letsencrypt,stweil/letsencrypt