Change mock_pkg_resource to create ebin directory

Change mock_pkg_resource to use rebar_test_utils:create_empty_app so
that an ebin directory is created which is a good expectation for a
package. Also revert the check in rebar_fetch:download_source to check
for an ebin directory before adding it to the code path for package
installs. If a package does not have an ebin directory it is probably
a good for an exception to be thrown.

src/rebar_fetch.erl

@@ -46,12 +46,7 @@ download_source(AppDir, Source) ->
                 code:del_path(filename:absname(filename:join(AppDir1, "ebin"))),
                 ec_file:remove(filename:absname(AppDir1), [recursive]),
                 ok = ec_file:copy(FromDir, filename:absname(AppDir1), [recursive]),
-                case ec_file:exists(filename:join(AppDir1, "ebin")) of
-                    true ->
-                        true = code:add_patha(filename:join(AppDir1, "ebin"));
-                    false ->
-                        ok
-                end,
+                true = code:add_patha(filename:join(AppDir1, "ebin")),
                 true
         end
     catch

test/mock_pkg_resource.erl

@@ -78,7 +78,7 @@ mock_download(Opts) ->
             App = binary_to_list(AppBin),
             filelib:ensure_dir(Dir),
             AppDeps = proplists:get_value({App,Vsn}, Deps, []),
-            {ok, AppInfo} = rebar_test_utils:create_app(
+            {ok, AppInfo} = rebar_test_utils:create_empty_app(
                 Dir, App, Vsn,
                 [element(1,D) || D  <- AppDeps]
             ),