[binutils-gdb] Fix py-value.exp failure on Python 3

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 7353f2470c2eda19c31c9fa44c315c7c69dea7c4 ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 7353f2470c2eda19c31c9fa44c315c7c69dea7c4

Fix py-value.exp failure on Python 3

I happened to notice that one test in py-value.exp did not work
properly with Python 3.  This patch fixes the problem.

2016-11-08  Tom Tromey  <tom@tromey.com>

	* gdb.python/py-value.exp (test_value_creation): Make "long" test
	depend on Python 2.