Bug 1117357 - Fix |mach bootstrap| for mobile/android on Mac OS X. r=gps

This does two things.  First, it aligns the brew formula name
(AndroidNdk) with the brew file name (android-ndk.rb).  Second, it
makes sure that we actually find the android-ndk.rb file.  I think
|mach bootstrap| always worked, due to a felicity where the working
directory always contained android-ndk.rb; but |python bootstrap.py|
failed because android-ndk.rb was downloaded to a temporary location
that was not included in the |brew install| command.

python/mozboot/bin/bootstrap.py

@@ -32,7 +32,7 @@ REPOSITORY_PATH_PREFIX = 'python/mozboot'
 
 REPOSITORY_PATHS = [
     'mozboot/__init__.py',
-    'mozboot/android-ndk-r8e.rb',
+    'mozboot/android-ndk.rb',
     'mozboot/android.py',
     'mozboot/base.py',
     'mozboot/bootstrap.py',