Support forcefully generating non-AB packages.

Force generate a non-A/B update package when requested.

Bug: 154344887
Test: ota_from_target_files.py --force_non_ab ...
Test: apply it as well

Change-Id: I5e81eb161722e07ef50081b6a16685cbc9963ae2
(cherry picked from commit 7169f754cc4b806c54a049b838355483575c1785)
Merged-In: I5e81eb161722e07ef50081b6a16685cbc9963ae2
diff --git a/tools/releasetools/blockimgdiff.py b/tools/releasetools/blockimgdiff.py
index 72f065d..8b6a690 100644
--- a/tools/releasetools/blockimgdiff.py
+++ b/tools/releasetools/blockimgdiff.py
@@ -1558,6 +1558,7 @@
     split_large_apks = []
     cache_size = common.OPTIONS.cache_size
     split_threshold = 0.125
+    assert cache_size is not None
     max_blocks_per_transfer = int(cache_size * split_threshold /
                                   self.tgt.blocksize)
     empty = RangeSet()