[network] disentangle main_node invocation of create/build/start for network_builders
[network] disentangle main_node invocation of create/build/start for network_builders

Closes: #4866
Approved by: davidiw

aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra