Fixing Windows tests

- Adding import path filter to exclude non-directories
  Otherwise kj will through exceptions
- Skipped AF_UNIX socket test
- Use default socket configuration when it doesn't matter the type of
socket used
- Open files with utf8 encoding (needed for text validation)
- Explictly call python executable when running external scripts
- Fix path creation to always use os.path.join
- Added timeout to client wait in some tests

- Some broken tests still remain (most likely asyncio related)

test/test_rpc.py

@@ -19,7 +19,7 @@ class Server(test_capability_capnp.TestInterface.Server):
 
 
 def test_simple_rpc_with_options():
-    read, write = socket.socketpair(socket.AF_UNIX)
+    read, write = socket.socketpair()
 
     _ = capnp.TwoPartyServer(write, bootstrap=Server())
     # This traversal limit is too low to receive the response in, so we expect
@@ -34,7 +34,7 @@ def test_simple_rpc_with_options():
 
 
 def test_simple_rpc_bootstrap():
-    read, write = socket.socketpair(socket.AF_UNIX)
+    read, write = socket.socketpair()
 
     _ = capnp.TwoPartyServer(write, bootstrap=Server(100))
     client = capnp.TwoPartyClient(read)