add hostname flag to setup testnet command

[charithabandi]

Adding this flag to support scenarios where the nodes doesn't have incremental IPs. For example the nodes deployed on the cloud has random public IP addresses that needs to be set in the config.toml as External address and for boot peers.

./.build/kwild setup testnet -v 2 -n 2 -u -o .net --db-owner 0xc89D42189f0450C2b2c3c61f58Ec5d628176A1E7 -H "54.208.120.196,54.208.120.197,54.208.120.198,54.208.120.199"

Generated config file:

# P2P related configuration
[p2p]
# address in host:port format to listen on for P2P connections
listen = '0.0.0.0:6600'
# enable peer exchange
pex = true
# bootnodes to connect to on startup
bootnodes = ['0226b3ff29216dac187cea393f8af685ad419ac9644e55dce83d145c8b1af213bd#secp256k1@54.208.120.196:6600', '02c57268fc884fa88425c7e5c19d3af263d1c64dd8b8f3f8c0fb31bb622d1fdab8#secp256k1@54.208.120.197:6601', '021072159608e8bfa10102cc74d3e1b533dfdf1904538a61de42811cc3066de014#secp256k1@54.208.120.198:6602', '029e578e4eb7d96fc770bacb4e7ba329d5611114c3831765427cb0e2d99cfee15f#secp256k1@54.208.120.199:6603']
# operate in private mode using a node ID whitelist
private = false
# allowed node IDs when in private mode
whitelist = []
# target number of connections to maintain
target_connections = 20
# external address in host:port format to advertise to the network
external_address = '54.208.120.196'