utils/env: Reinstore old AndroidTarget working directory

As mentionned in ARM-software/devlib#225,
using /sdcard causes some issues with the HiKey960. As we haven't
had any issues with using /data/local/tmp/ as a devlib working
directory, we now enforce the use of this directory.

libs/utils/env.py

@@ -525,6 +525,7 @@ def _init_target(self, force = False):
             self.target = devlib.AndroidTarget(
                     platform = platform,
                     connection_settings = self.__connection_settings,
+                    working_directory = '/data/local/tmp/devlib-target',
                     load_default_modules = False,
                     modules = self.__modules)
         elif platform_type.lower() == 'host':