devtool: use cp instead of shutil.copytree
Copied layers with 'cp -a' instead of calling shutil.copytree as
copytree fails to copy broken symlinks.
More pythonic fix would be to use copytree with 'ignore' parameter,
but this could slow down copying complex directory structures.
[YOCTO #8825]
(From OE-Core master rev:
e5b841420b9fdd33829f7665a62cd06a3017f7e6)
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
