python: explicitly disable bluetooth.h check

* bluetooth.h is autodetected from sysroot and influences 2 python files:
  /usr/include/python2.7/pyconfig-32.h
  /usr/lib/python2.7/lib-dynload/_socket.so
* it doesn't link with bluez, so it wasn't detected by
  test-dependencies.sh, but still causes undeterministic builds and
  should be fixed
* we can use PACKAGECONFIG, but I don't expect many people to use bt
  support in python-socket

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>