fix android_package_directory for ones already installed android sdk

ruboto setup now detect the installed android sdk path before downloading a new one into HOME.
in my installation: 

>asakawa at ArchLinux in ~/Projects
$ ruboto setup
Java runtime             : Found
Java Compiler            : Found
Apache ANT               : Found
Android Package Installer: Found
Android Emulator         : Found
Android SDK Command adb  : Found
Android SDK Command dx   : Found
Platform SDK android-10  : Found
    *** Ruboto setup is OK! ***
You are missing some paths.  Execute these lines to add them:
    export PATH="/home/asakawa/Softwares/adt-bundle-linux-x86_64/sdk/build-tools/android-4.2.2:$PATH"
Would you like to append these lines to your configuration script? (Y/n):