Exclude bug_map from the sepolicy_freeze_test.

The bug_map file is only used whitelisting known test failures.  It
needs to change fairly often to fix new failures and it doesn't affect
users, so it shouldn't matter if it diverges from prebuilts.

Test: Enable this test and build with and without different bug_maps.
Change-Id: I9176a6c7e9f7852a0cd7802fd121b1e86b216b22