QA: add RPC tests for error reporting of "signrawtransaction"

Tests error reporting of transaction signing via RPC call "signrawtransaction".

Expected results:

Test 1: create and sign a valid raw transaction with one input:

• 1) The transaction has a complete set of signatures
• 2) No script verification error occurred

Test 2: create and sign a raw transaction with one valid, one invalid and one missing input script:

• 3) The transaction has no complete set of signatures
• 4) Two script verification errors occurred
• 5) Script verification errors have certain properties ("txid", "vout", "scriptSig", "sequence", "error")
• 6) The verification errors refer to the invalid (vin 1) and missing input (vin 2)