Add original RootTools library.

Version 23fe96a2219005059b35e39a1fd435fc9acccb7c.
Rewrite su access to use RootTools.

With some code from libsuperuser sprinkeled in.

This means it should now run on enforcing Android L (with a context), as
well as on CM11 (where a context is not supported).
RootTools: Do not apply retries to DENY response.

See https://github.com/Stericson/RootTools/issues/27.
Make sure the shells are closed at the end.