devtool.py: track to clean devtool.conf in test_create_workspace
`devtool create-workspace' would create devtool.conf, so track to
clean it up. Otherwise, this devtool.conf file would mess things up.
e.g.
oe-selftest -r devtool && oe-selftest -r devtool -j 2
AssertionError: '/PROJ_DIR/build-selftest-st-15753/workspace/conf/layer.conf' does not exist : Workspace directory not created
This is because the devtool.conf is also copied to build-selftest-st-xxxx
directory, resulting in devtool to create and use workspace specified
in this file.
Signed-off-by: Chen Qi <Qi.Chen@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
