selftest/bblayers.py: Remove harcoded recipe files

selftest/bblayers.py: Remove harcoded recipe files

Currently the recipe files are hardcoded and if the recipe
change the version, the test will fail.

This will change from using a harcoded file to look for the
file using bitbake-layers. Now, just the recipe name must
be specified.

(From OE-Core rev: 1ee24e435353d93374895eead81fb281e1338739)

Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>