pyln-testing: allow elementsd/liquid tests to proceed

Most recent version of elementsd is still v0.18.0. iiuc they're in the
process of updating it.

contrib/pyln-testing/pyln/testing/fixtures.py

@@ -127,10 +127,16 @@ def bitcoind(directory, teardown_checks):
 
     info = bitcoind.rpc.getnetworkinfo()
 
-    if info['version'] < 200100:
+    # FIXME: include liquid-regtest in this check after elementsd has been
+    # updated
+    if info['version'] < 200100 and env('TEST_NETWORK') != 'liquid-regtest':
         bitcoind.rpc.stop()
         raise ValueError("bitcoind is too old. At least version 20100 (v0.20.1)"
                          " is needed, current version is {}".format(info['version']))
+    elif info['version'] < 160000:
+        bitcoind.rpc.stop()
+        raise ValueError("elementsd is too old. At least version 160000 (v0.16.0)"
+                         " is needed, current version is {}".format(info['version']))
 
     # At 0.21, createwallet needed, but in 0.20.1 createwallet then broke
     # calls to getnewaddress with "bitcoin.rpc.JSONRPCError: {'code': -19, 'message': 'Wallet file not specified (must request wallet RPC through /wallet/<filename> uri-path).'}"