Merge #20168: contrib: Fix gen_key_io_test_vectors.py imports

fa68755 contrib: Fix gen_key_io_test_vectors.py imports (MarcoFalke)

Pull request description:

  The script currently fails with

  ```
  Traceback (most recent call last):
    File "./gen_key_io_test_vectors.py", line 18, in <module>
      from segwit_addr import bech32_encode, decode, convertbits, CHARSET
  ImportError: cannot import name 'decode' from 'segwit_addr'
  ```

  Fix that.
  Also, unrelated cleanup to use the `bytearray.hex()` method instead of importing a library. https://docs.python.org/3.5/library/stdtypes.html#bytes.hex

ACKs for top commit:
  theStack:
    tested ACK fa68755

Tree-SHA512: 45ff7d710de3d0ef5ac6d91543cff0edff6189d2cd00b0f8889f4361e66ef1825f12aea9e71d62038c14a7a531bfc95ffe9a1df83b85aa7f3dd666df07a6be81

Author: fanquake

contrib/testgen/gen_key_io_test_vectors.py

@@ -15,8 +15,7 @@
 from itertools import islice
 from base58 import b58encode_chk, b58decode_chk, b58chars
 import random
-from binascii import b2a_hex
-from segwit_addr import bech32_encode, decode, convertbits, CHARSET
+from segwit_addr import bech32_encode, decode_segwit_address, convertbits, CHARSET
 
 # key types
 PUBKEY_ADDRESS = 0
@@ -109,7 +108,7 @@ def is_valid(v):
 def is_valid_bech32(v):
     '''Check vector v for bech32 validity'''
     for hrp in ['bc', 'tb', 'bcrt']:
-        if decode(hrp, v) != (None, None):
+        if decode_segwit_address(hrp, v) != (None, None):
             return True
     return False
 
@@ -141,9 +140,7 @@ def gen_valid_vectors():
             rv, payload = valid_vector_generator(template)
             assert is_valid(rv)
             metadata = {x: y for x, y in zip(metadata_keys,template[3]) if y is not None}
-            hexrepr = b2a_hex(payload)
-            if isinstance(hexrepr, bytes):
-                hexrepr = hexrepr.decode('utf8')
+            hexrepr = payload.hex()
             yield (rv, hexrepr, metadata)
 
 def gen_invalid_base58_vector(template):