oeqa/selftest/recipetool: Fix appendfile_binary test on opensuse131

oeqa/selftest/recipetool: Fix appendfile_binary test on opensuse131

On OpenSUSE 13.1, /bin/ls is a symlink to /usr/bin/ls. This means the
test doesn't use a binary file an fails on that system.

Ensure we resolve any symlink using readlink to avoid this failure.

======================================================================
FAIL: test_recipetool_appendfile_binary (oeqa.selftest.recipetool.RecipetoolTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/pokybuild/yocto-autobuilder/yocto-worker/nightly-oe-selftest/build/meta/lib/oeqa/selftest/recipetool.py", line 115, in test_recipetool_appendfile_binary
    self.assertIn('WARNING: ', result.output)
AssertionError: 'WARNING: ' not found in 'Parsing recipes..done.\nNOTE: Writing append file /tmp/recipetoolqai0NY8l/recipes-core/coreutils/coreutils_8.23.bbappend\nNOTE: Copying /bin/ls to /tmp/recipetoolqai0NY8l/recipes-core/coreutils/coreutils/ls'

[YOCTO #7920]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>