Update testnet bootnode dns name (#1712)

# Description
Update the DNS name of bootnodes to unify the deployment. 

Each bootnode have 3 port exposed: `30333, 30334, 443`. Before, we had
different DNS names for `30333, 30334` and `443` ports. It may confuse
people and give the impression that it is two different nodes. Fixing it
by using a single domain for all