Bug 1108771 - Part 2: Implement |mach bootstrap| for mobile/android on Debian-like systems. r=gps

This adds a generic android Python module that handles:

* downloading and unpacking Google's Android SDK and NDK bundles;
* using the |android| tool to install additional Android packages;
* printing a mozconfig snippet suitable for mobile/android builds.

python/mozboot/bin/bootstrap.py

@@ -32,6 +32,7 @@ REPOSITORY_PATH_PREFIX = 'python/mozboot'
 
 REPOSITORY_PATHS = [
     'mozboot/__init__.py',
+    'mozboot/android.py',
     'mozboot/base.py',
     'mozboot/bootstrap.py',
     'mozboot/centos.py',