* We search first in specified folders by the user (they can browse to
the android SDK and java JDK).
* If the tools we want aren't found there, we look relative to the UI
as we now distribute the required tools with windows builds.
* If we still don't find them, we prefer to look in PATH since the user
has 'opted in' to any tools found in there. If the tool isn't in PATH
either then we look relative to known environment variables.