Auto merge of #4398 - mdr0id:rpc_cross_platform_updates, r=str4d

Update RPCs to support cross platform testing

This PR is used to add support for cross platform testing per host. Specifically, Windows RPCs.

Notes from upstream on dbm.dumb : https://github.com/bitcoin/bitcoin/pull/8834/files

qa/rpc-tests/test_framework/blockstore.py

@@ -7,7 +7,7 @@ from .mininode import CBlock, CBlockHeader, CBlockLocator, CTransaction, msg_blo
 
 import sys
 import io
-import dbm
+import dbm.dumb as dbm
 
 class BlockStore():
     def __init__(self, datadir):

qa/rpc-tests/test_framework/netutil.py

@@ -6,7 +6,6 @@
 # Linux network utilities
 import sys
 import socket
-import fcntl
 import struct
 import array
 import os
@@ -88,6 +87,8 @@ def all_interfaces():
     '''
     Return all interfaces that are up
     '''
+    import fcntl
+    
     is_64bits = sys.maxsize > 2**32
     struct_size = 40 if is_64bits else 32
     s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

qa/rpc-tests/test_framework/util.py

@@ -137,7 +137,7 @@ def initialize_chain(test_dir):
             shutil.rmtree("cache")
 
     if not os.path.isdir(os.path.join("cache", "node0")):
-        devnull = open("/dev/null", "w+")
+        devnull = open(os.devnull, "w+")
         # Create cache directories, run bitcoinds:
         for i in range(4):
             datadir=initialize_datadir("cache", i)
@@ -240,7 +240,7 @@ def start_node(i, dirname, extra_args=None, rpchost=None, timewait=None, binary=
     ])
     if extra_args is not None: args.extend(extra_args)
     bitcoind_processes[i] = subprocess.Popen(args)
-    devnull = open("/dev/null", "w+")
+    devnull = open(os.devnull, "w+")
     if os.getenv("PYTHON_DEBUG", ""):
         print("start_node: bitcoind started, calling bitcoin-cli -rpcwait getblockcount")
     subprocess.check_call([ os.getenv("BITCOINCLI", "bitcoin-cli"), "-datadir="+datadir] +