Better stake adjustment in pytest

[Longarithm]

Description

Instead of this sophisticated pattern,

        default_stake = 50000000000000000000000000000000
        stake_delta = 5000000000000000000000000000000
...
start_cluster(...,
       ["validators", 0, "amount", str(default_stake + stake_delta)],
       ["validators", 1, "amount", str(default_stake - stake_delta)],
       ["records", 0, "Account", "account", "locked", str(default_stake + stake_delta)],
       ["records", 2, "Account", "account", "locked", str(default_stake - stake_delta)]

pass simpler arguments to init with stakes other than default_stake, without breaking validators and total_supply.