[Storage] Use unwrap instead of propagating errors in unit tests
[Storage] Use unwrap instead of propagating errors in unit tests

This makes it much easier to locate where the error comes from when
debugging unit test errors -- simplying adding RUST_BACKTRACE=1 when
running the tests.

Closes: #1990
Approved by: zekun000

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