Fix default binary in p2p tests to use environment variable

qa/rpc-tests/maxblocksinflight.py

@@ -77,7 +77,8 @@ class TestManager(NodeConnCB):
         
 class MaxBlocksInFlightTest(BitcoinTestFramework):
     def add_options(self, parser):
-        parser.add_option("--testbinary", dest="testbinary", default="bitcoind",
+        parser.add_option("--testbinary", dest="testbinary",
+                          default=os.getenv("BITCOIND", "bitcoind"),
                           help="Binary to test max block requests behavior")
 
     def setup_chain(self):

qa/rpc-tests/test_framework.py

@@ -155,9 +155,11 @@ class ComparisonTestFramework(BitcoinTestFramework):
         self.num_nodes = 2
 
     def add_options(self, parser):
-        parser.add_option("--testbinary", dest="testbinary", default="bitcoind",
+        parser.add_option("--testbinary", dest="testbinary",
+                          default=os.getenv("BITCOIND", "bitcoind"),
                           help="bitcoind binary to test")
-        parser.add_option("--refbinary", dest="refbinary", default="bitcoind",
+        parser.add_option("--refbinary", dest="refbinary",
+                          default=os.getenv("BITCOIND", "bitcoind"),
                           help="bitcoind binary to use for reference nodes (if any)")
 
     def setup_chain(self):