init: move asmap code earlier in init process

and update feature_asmap.py and test_runner.py

This commit moves the asmap init.cpp code from the end of "Step 12: start node"
to "Step 6: network initialization" to provide feedback on passing an -asmap
config arg much more quickly. This change speeds up the feature_asmap.py
functional test file from 60 to 5 seconds by accelerating the 2 tests that use
`assert_start_raises_init_error`.

Credit to Wladimir J. van der Laan for the suggestion.

test/functional/test_runner.py

@@ -101,7 +101,6 @@ BASE_SCRIPTS = [
     'rpc_txoutproof.py',
     'wallet_listreceivedby.py',
     'wallet_abandonconflict.py',
-    'feature_asmap.py',
     'feature_csv_activation.py',
     'rpc_rawtransaction.py',
     'wallet_address_types.py',
@@ -207,6 +206,7 @@ BASE_SCRIPTS = [
     'p2p_dos_header_tree.py',
     'p2p_unrequested_blocks.py',
     'feature_includeconf.py',
+    'feature_asmap.py',
     'rpc_deriveaddresses.py',
     'rpc_deriveaddresses.py --usecli',
     'rpc_scantxoutset.py',