[cluster-test] Fix account minting into proper async fn
[cluster-test] Fix account minting into proper async fn

Account minting did something unexplainable with creating new runtime and spawning new thread. This diff fixes this into a parallel future

Closes: #3994
Approved by: ankushagarwal

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