[runtime] [test] Fix using %python path

[runtime] [test] Fix using %python path

Fix the newly-added tests to use %python substitution in order to use
the correct path to Python interpreter.  Otherwise, they fail on NetBSD
where there is no 'python', just 'pythonX.Y'.

Differential Revision: https://reviews.llvm.org/D56048

llvm-svn: 350001