Adding assert_ndk_version for Android from Jørgen Tjernø.

- Ceres now requires Android NDK version >= r9d to compile, Jørgen's
  script allows a clean way to verify this condition is met before
  trying to compile for Android.
- Note that this is a modified version of the original script, which
  adds support for versions >= 10, and fixes extraction of the version
  number now that the architecture is also included.

Change-Id: Icd7ffd25407bcf29af007e30b5da5d18eb799adf