bitbake: prserv: fix ResourceWarning due to unclosed socket

With PRSERV_HOST = "localhost:0", this message would occasionally pop up
during the initial cache read:

WARNING: /home/matic/ambayocto/poky/bitbake/lib/bb/cache.py:446: ResourceWarning: unclosed <socket.socket fd=10, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('127.0.0.1', 45655)>
  value = pickled.load()

The file location stated is irrelevant; it just happens to be wherever
CPython decides to run the garbage collector. The issue is that after we
fork off a PRServer, self.socket is also duplicated. The parent side of
it also needs to be closed.

(Bitbake rev: cd970c9efa805ec3e7ba952df1701b347441ec7b)

Signed-off-by: Gavin Li <gavin@matician.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/prserv/serv.py

@@ -243,6 +243,7 @@ class PRServer(SimpleXMLRPCServer):
         try:
             pid = os.fork()
             if pid > 0:
+                self.socket.close() # avoid ResourceWarning in parent
                 return pid
         except OSError as e:
             raise Exception("%s [%d]" % (e.strerror, e.errno))