Add pyramid level check in subgop unit test

This patch extends subgop unit test to validate pyramid level
and corresponding qindex assignment of each frame.

Change-Id: I5c18e513aaab86c11a4f0e6af0544419f4d183e2

av1/decoder/decoder.c

diff --git a/av1/decoder/decoder.c b/av1/decoder/decoder.c
index 608b1a7..c13fa15 100644
--- a/av1/decoder/decoder.c
+++ b/av1/decoder/decoder.c
@@ -55,6 +55,7 @@
   subgop_stats->show_existing_frame[subgop_stats->stat_count] =
       cm->show_existing_frame;
   subgop_stats->show_frame[subgop_stats->stat_count] = cm->show_frame;
+  subgop_stats->qindex[subgop_stats->stat_count] = cm->quant_params.base_qindex;
   assert(subgop_stats->stat_count < MAX_SUBGOP_STATS_SIZE);
   subgop_stats->stat_count++;
 }