manifest: Add forked toybox

It will be used for some devices like Sony Open devices
(replacing busybox).

Signed-off-by: Humberto Borba <humberos@gmail.com>
Change-Id: I0fabfdc17743edda87738913b9658f80b86fe8ee

default.xml

@@ -250,7 +250,7 @@
   <project path="external/tinycompress" name="android_external_tinycompress" remote="omnirom" revision="android-6.0" groups="pdk" />
   <project path="external/tinyxml" name="platform/external/tinyxml" groups="pdk" />
   <project path="external/tinyxml2" name="platform/external/tinyxml2" groups="pdk" />
-  <project path="external/toybox" name="platform/external/toybox" groups="pdk" />
+  <project path="external/toybox" name="android_external_toybox" remote="omnirom" revision="android-6.0" groups="pdk" />
   <project path="external/tremolo" name="platform/external/tremolo" groups="pdk" />
   <project path="external/v8" name="platform/external/v8" groups="pdk" />
   <project path="external/valgrind" name="platform/external/valgrind" groups="pdk" />