Android SDK Updates and Bug Fixes

Points to discuss with @joshk:

* go for 041336389af6b335b8099970562df00c7592cee9 ?
* preinstall `android-L`, the [L Developer Preview](http://developer.android.com/preview/api-overview.html).
* maybe reduce the VM size, by installing less (or even no) system images. Note that preinstalling popular system images shaves build time for projects that are using related emulators.
* Already activate `maven-rescue` recipe ? This part is not final, but it might be interesting to gather some first feedbacks during the beta phase. See travis-ci/travis-ci#2280.
* Update the docs (android-wait-for-emulator, new versions).