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)

qa/pull-tester/rpc-tests.sh

@@ -22,6 +22,7 @@ testScripts=(
     'txn_doublespend.py'
     'txn_doublespend.py --mineblock'
     'getchaintips.py'
+    'rawtransactions.py'
     'rest.py'
     'mempool_spendcoinbase.py'
     'mempool_coinbase_spends.py'
@@ -29,7 +30,7 @@ testScripts=(
     'zapwallettxes.py'
     'proxy_test.py'
     'merkle_blocks.py'
-    'rawtransactions.py'
+    'signrawtransactions.py'
 #    'forknotify.py'
     'maxblocksinflight.py'
     'invalidblockrequest.py'