Add a --descriptors option to various tests

Adds a --descriptors option globally to the test framework. This will
make the test create and use descriptor wallets. However some tests may
not work with this.

Some tests are modified to work with --descriptors and run with that
option in test_runer:
* wallet_basic.py
* wallet_encryption.py
* wallet_keypool.py
* wallet_keypool_topup.py
* wallet_labels.py
* wallet_avoidreuse.py

test/functional/test_framework/key.py

@@ -8,6 +8,8 @@ keys, and is trivially vulnerable to side channel attacks. Do not use for
 anything but tests."""
 import random
 
+from .address import byte_to_base58
+
 def modinv(a, n):
     """Compute the modular inverse of a modulo n
 
@@ -384,3 +386,14 @@ class ECKey():
         rb = r.to_bytes((r.bit_length() + 8) // 8, 'big')
         sb = s.to_bytes((s.bit_length() + 8) // 8, 'big')
         return b'\x30' + bytes([4 + len(rb) + len(sb), 2, len(rb)]) + rb + bytes([2, len(sb)]) + sb
+
+def bytes_to_wif(b, compressed=True):
+    if compressed:
+        b += b'\x01'
+    return byte_to_base58(b, 239)
+
+def generate_wif_key():
+    # Makes a WIF privkey for imports
+    k = ECKey()
+    k.generate()
+    return bytes_to_wif(k.get_bytes(), k.is_compressed)