[test] Add coverage to estimaterawfee and estimatesmartfee

This adds light functional coverage to estimaterawfee - a subset of
the testing applied to estimatesmartfee, and argument validation
testing to both estimaterawfee and estimatesmartfee.

One valid estimatesmartfee signature test is commented out because it
fails currently.

test/functional/test_runner.py

@@ -191,6 +191,7 @@ BASE_SCRIPTS = [
     'wallet_resendwallettransactions.py',
     'wallet_fallbackfee.py',
     'feature_minchainwork.py',
+    'rpc_estimatefee.py',
     'rpc_getblockstats.py',
     'wallet_create_tx.py',
     'p2p_fingerprint.py',