Refactor: Provide lightningd in constructor

The fixtures in `tests/fixtures.py` modifies the path to
`lightningd/lightningd`.

I've adapted `pyln-testing` to accept an executable in the constructor.
This approach is more transparant and allows us to use the executable
path to query the version in the constructor.

contrib/pyln-testing/pyln/testing/utils.py

@@ -596,10 +596,11 @@ class LightningD(TailableProc):
             port=9735,
             random_hsm=False,
             node_id=0,
+            executable=None,
     ):
         # We handle our own version of verbose, below.
         TailableProc.__init__(self, lightning_dir, verbose=False)
-        self.executable = 'lightningd'
+        self.executable = "lightningd" if executable is None else executable
         self.lightning_dir = lightning_dir
         self.port = port
         self.cmd_prefix = []
@@ -759,6 +760,7 @@ class LightningNode(object):
                  db=None, port=None, grpc_port=None, disconnect=None, random_hsm=None, options=None,
                  jsonschemas={},
                  valgrind_plugins=True,
+                 executable=None,
                  **kwargs):
         self.bitcoin = bitcoind
         self.executor = executor
@@ -781,6 +783,7 @@ class LightningNode(object):
         self.daemon = LightningD(
             lightning_dir, bitcoindproxy=bitcoind.get_proxy(),
             port=port, random_hsm=random_hsm, node_id=node_id,
+            executable=executable,
         )
 
         self.disconnect = disconnect

tests/fixtures.py

@@ -16,6 +16,9 @@ def node_cls():
 
 class LightningNode(utils.LightningNode):
     def __init__(self, *args, **kwargs):
+        # Yes, we really want to test the local development version, not
+        # something in out path.
+        kwargs["executable"] = "lightningd/lightningd"
         utils.LightningNode.__init__(self, *args, **kwargs)
 
         # This is a recent innovation, and we don't want to nail pyln-testing to this version.
@@ -50,10 +53,6 @@ class LightningNode(utils.LightningNode):
             accts_db = self.db.provider.get_db('', 'accounts', 0)
             self.daemon.opts['bookkeeper-db'] = accts_db.get_dsn()
 
-        # Yes, we really want to test the local development version, not
-        # something in out path.
-        self.daemon.executable = 'lightningd/lightningd'
-
 
 class CompatLevel(object):
     """An object that encapsulates the compat-level of our build.