toaster: localhostbecontroller Don't clear out toaster custom layer dir

toaster: localhostbecontroller Don't clear out toaster custom layer dir

We may have a recipe which is based on a custom image recipe that has
already been built so keep the recipe file around so that it can be read
by the generate recipe function.

Signed-off-by: Michael Wood <michael.g.wood@intel.com>
Signed-off-by: Elliot Smith <elliot.smith@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>