feat(iroha-connector): fully test Iroha's getPendingTransaction query

[hanxu12]

Is your feature request related to a problem? Please describe.
Iroha's query, getPendingTransaction, is not fully tested. There is an issue with producing a pending transaction: the code will get stuck and fail the test suite. This seems to be an issue with Iroha ledger itself instead of the Iroha Javascript library. Since a pending transaction cannot be generately smoothly within the test case, getPendingTransaction is not tested.

Describe the solution you'd like
See when Iroha team resolves the issue with Iroha's difficulty in producing a pending transaction. Once we are able to produce a pending transaction in the test case, we can validate the pending transaction via getPendingTrasaction query.

Describe alternatives you've considered
N/A

Additional context
N/A