[tests] Speed up rpc_fundrawtransaction.py

Most of the time in rpc_fundrawtransaction.py is spent waiting for
unconfirmed transactions to propagate. Net processing adds a poisson
random delay to the time it will INV transactions with a mean interval
of 5 seconds.

Instead just generate the block on the node that sent the transaction:

rpc_fundrawtransaction.py is not intended to be a test for transaction
relay, so it's ok to do this.

[tests] Use -whitelist in rpc_fundrawtransaction.py

Makes tx relay faster

[tests] Don't stop-start unnecessarily in rpc_fundrawtransaction.py

This was only added in c1dde3a949b36ce9c2155777b3fa1372e7ed97d8 to match
behaviour when encryptwallet would restart the node. It's not required
for the test (and slows things down).

This is a backport of Core PR17340