Let mock_env return a contract address that is compatible with MockApi

[webmaster128]

While this only solves part of the problem, it allows a huge portion of users to keep their tests unchanged.

[chipshort]

Yes, this is a simpler middleground solution that I also thought about, but (as you can see) also causes some test failures when the tests assume that the address is equal to MOCK_CONTRACT_ADDRESS.
We should probably also adjust at least mock_dependencies_with_balance in a similar way.
Maybe even mock_dependencies_with_balances, but that would probably cause other tests to fail.

[webmaster128]

Okay, seems to be better now.

• MOCK_CONTRACT_ADDR is the actual bech32 address
• Added some comments for BankQuerier address management. No change required here as far as I can tell as the strings in the map are supposed to be the addresses already.
• Applied the same changes to cosmwasm-vm

[chipshort]

Nice. This should cover most cases while not failing tests unnecessarily.