Tests: Use self.chain instead of 'regtest' in almost all current tests

test/functional/feature_abortnode.py

@@ -29,7 +29,7 @@ class AbortNodeTest(BitcoinTestFramework):
         datadir = get_datadir_path(self.options.tmpdir, 0)
 
         # Deleting the undo file will result in reorg failure
-        os.unlink(os.path.join(datadir, 'regtest', 'blocks', 'rev00000.dat'))
+        os.unlink(os.path.join(datadir, self.chain, 'blocks', 'rev00000.dat'))
 
         # Connecting to a node with a more work chain will trigger a reorg
         # attempt.