[staleblock_test] Free markers after use
[staleblock_test] Free markers after use

Free markers through fdb_free_snap_markers
after use to avoid heap-use-after-free issue
as detected by thread sanitizer.

Change-Id: Id34281cb2d9c91d4d8934beefb2f186aea1bc035
11:43:20 WARNING: ThreadSanitizer: heap-use-after-free (pid=116815)
11:43:20   Read of size 8 at 0x7d300000bfb0 by main thread:
11:43:20     #0 superblock_recovery_test() crtstuff.c (staleblock_test+0x0000004d1be2)
11:43:20     #1 main crtstuff.c (staleblock_test+0x0000004d2662)
11:43:20
11:43:20   Previous write of size 8 at 0x7d300000bfb0 by main thread:
11:43:20     #0 free <null> (staleblock_test+0x00000046136b)
11:43:20     #1 fdb_free_snap_markers /home/couchbase/jenkins/workspace/forestdb-threadsanitizer-master/forestdb/src/forestdb.cc:7700 (staleblock_test+0x00000050e49f)
11:43:20     #2 superblock_recovery_test() crtstuff.c (staleblock_test+0x0000004d1bbc)
11:43:20     #3 main crtstuff.c (staleblock_test+0x0000004d2662)
Reviewed-on: http://review.couchbase.org/62812
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Tested-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

couchbase/forestdb,wurikiji/forestdb,wurikiji/forestdb,hisundar/forestdb,couchbase/forestdb,hisundar/forestdb