De-duplicate test-utils

[cbeck88]

Numerous core crates come also with a "test-utils" crate (although sometimes the test-utils come in a submodule).

mc-transaction-core-test-utils mc-ledger-db::test_utils mobilecoind-test-utils

Some of these test-utils crates have a lot of very similar (possibly the same?) functionality:

In mc-transaction-core-test-utils:

• initialize_ledger takes a ledger db object and adds a bunch of test blocks to it
• create_transaction creates a test transaction
• get_blocks creates a list of test blocks

In mc-transaction-std, we have separate, slightly different versions of create_transaction in the tests module.

In mc-ledger-db-test-utils, get_test_ledger_blocks is almost the same transaction-core-test-utils::get_blocks.

In ledger/sync/src/test_app/main.rs we have functions like _make_ledger_long which takes a ledger and adds a bunch of blocks to it. This is almost exactly the same as mc_transaction_core_test_utils::initialize_ledger.

In mobilecoind::test_utils, add_block_to_ledger_db is almost the same as mc-transaction-core-test-utils::initialize_ledger and the _make_ledger_long.

We could likely have 2 or 3 functions instead of 10. This would make it much easier to read and maintain this test code, if we just had one flexible "add blocks to ledger" function instead of 3 or 4 variations on a theme that no one can remember the differences between. It would also make it much easier in the future when we have to make changes to TxOut or TransactionBuilder, which will happen whenever we want to ship new features into the blockchain.

[remoun]

I did some of this in #2052, which I hope to merge next week.