Merge #15485: add rpc_misc.py, mv test getmemoryinfo, add test mallocinfo

f13ad1cae0 modify test for memory locked in case locking pages failed at some point (Adam Jonas)
2fa85ebd1c add rpc_misc.py, mv test getmemoryinfo, add test mallocinfo (Adam Jonas)

Pull request description:

  Creating the `rpc_misc.py` functional test file to add space for adding tests to a file that doesn't have a lot of coverage.
    - Removing the `getmemoryinfo()` smoke test from wallet basic rather than moving it to keep the wallet decoupled. Feel like testing for reasonable memory allocation values should suffice.
    - Adding coverage for `mallocinfo()`. Introduced standard lib XML parser since the function exports an XML string that describes the current state of the memory-allocation implementation in the caller.

Tree-SHA512: ced30115622916c88d1e729969ee331272ec9f2881eb36dee4bb7331bf633a6810a57fed63a0cfaf86de698edb5162e6a035efd07c89ece1df56b69d61288072

test/functional/wallet_basic.py

@@ -11,7 +11,6 @@ from test_framework.util import (
     assert_array_result,
     assert_equal,
     assert_fee_amount,
-    assert_greater_than,
     assert_raises_rpc_error,
     connect_nodes_bi,
     sync_blocks,
@@ -84,13 +83,8 @@ class WalletTest(BitcoinTestFramework):
         assert_equal(txout['value'], 50)
 
         # Send 21 BTC from 0 to 2 using sendtoaddress call.
-        # Locked memory should increase to sign transactions
-        self.log.info("test getmemoryinfo")
-        memory_before = self.nodes[0].getmemoryinfo()
         self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 11)
         mempool_txid = self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 10)
-        memory_after = self.nodes[0].getmemoryinfo()
-        assert_greater_than(memory_after['locked']['used'], memory_before['locked']['used'])
 
         self.log.info("test gettxout (second part)")
         # utxo spent in mempool should be visible if you exclude mempool