Make Android SDK Image smaller

[samtstern]

Android SDK image is 4.5GB bigger than Ubuntu image, but the Android SDK folder is only 2GB.

Android SDK size:

  vagrant@da29b6195f58:/$ du -sh ~/Android/Sdk
    2.0G        /home/vagrant/Android/Sdk

Image sizes:

vagrant@vagrant-ubuntu-trusty-64:~$ docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
samtstern/android-studio   latest              235a23a2009a        About an hour ago   5.589 GB
samtstern/android-base     latest              b46a4932c7e0        About an hour ago   4.74 GB
ubuntu                     trusty              5ba9dab47459        2 weeks ago         188.3 MB
ubuntu                     14.04               5ba9dab47459        2 weeks ago         188.3 MB
ubuntu                     14.04.1             5ba9dab47459        2 weeks ago         188.3 MB
ubuntu                     latest              5ba9dab47459        2 weeks ago         188.3 MB