ITS: test_preview_zoom: Fix missing camera frames

Problem: MediaRecorder drop 1 or more camera frames upon calling
MediaRecorder.stop() on some devices.

Workaround: Add green buffer frames at the end of recorded camera
frames. This way green buffer frames would be droped due to calling
MediaRecorder.stop(). On Python side, green buffer frames are removed
before test verification.

Bug:  348349231
Test: test_preview_zoom.py
Flag: TEST_ONLY
Change-Id: I2f4e28972f759f165143aa76c621f186c9b2ba1f
(cherry picked from commit 2856c62757602ae970a1a995fcc209accbf4d74a)