Make `test_save_animation_smoketest` actually run

Marked mencoder as KnownFailure
added test_animation to default_test_modules so the tests run
added try-catch block to test_animation to deal with strange
import errors coming out of numpy.  See issue #1891.
added libav-tools to the packages installed so that more of the
animation smoke tests will run.
Merge pull request #2679 from tacaswell/fix_animation_tests

Make `test_save_animation_smoketest` actually run