Add call to testutil_cleanup to avoid memory leak

FAIL: test_wt4156_metadata_salvage

==================================

[1535634261:577553][6841:0x7fe57d9e7740], file:WiredTiger.wt, WT_CURSOR.next: __wt_block_read_off, 282: WiredTiger.wt: read checksum error for 28672B block at offset 208896: calculated block checksum of 2610979647 doesn't match expected checksum of 236927266: Successful return: 0

...

[1535634261:587150][6841:0x7fe57d9e7740], file:WiredTiger.wt, WT_CURSOR.next: __wt_block_read_off, 302: WiredTiger.wt: fatal read error: WT_ERROR: non-specific WiredTiger error: WT_ERROR: non-specific WiredTiger error

[1535634261:587159][6841:0x7fe57d9e7740], file:WiredTiger.wt, WT_CURSOR.next: __wt_panic, 523: the process must exit and restart: WT_PANIC: WiredTiger library panic: WT_PANIC: WiredTiger library panic

[1535634261:587186][6841:0x7fe57d9e7740], txn-recover: __wt_txn_recover, 721: Recovery failed: WT_PANIC: WiredTiger library panic: WT_PANIC: WiredTiger library panic

[1535634261:587266][6841:0x7fe57d9e7740], connection: __wt_cache_destroy, 384: cache server: exiting with 3 pages in memory and 0 pages evicted: Successful return: 0

[1535634261:587276][6841:0x7fe57d9e7740], connection: __wt_cache_destroy, 389: cache server: exiting with 53823 image bytes in memory: Successful return: 0

[1535634261:587282][6841:0x7fe57d9e7740], connection: __wt_cache_destroy, 393: cache server: exiting with 54391 bytes in memory: Successful return: 0

copy: rm -rf ./WT_TEST.test_wt4156_metadata_salvage.SAVE; mkdir ./WT_TEST.test_wt4156_metadata_salvage.SAVE; cp -p WT_TEST.test_wt4156_metadata_salvage/* ./WT_TEST.test_wt4156_metadata_salvage.SAVE;

corrupt metadata

copy: cp -p WT_TEST.test_wt4156_metadata_salvage/WiredTiger.wt ./WT_TEST.test_wt4156_metadata_salvage.SAVE/WiredTiger.wt.CORRUPT

test_wt4156_metadata_salvage: FAILED: wt_open_corrupt/345: ret == WT_TRY_SALVAGE

process aborting

copy: rm -rf ./WT_TEST.test_wt4156_metadata_salvage.SAVE; mkdir ./WT_TEST.test_wt4156_metadata_salvage.SAVE; cp -p WT_TEST.test_wt4156_metadata_salvage/* ./WT_TEST.test_wt4156_metadata_salvage.SAVE;

corrupt metadata

copy: cp -p WT_TEST.test_wt4156_metadata_salvage/WiredTiger.wt ./WT_TEST.test_wt4156_metadata_salvage.SAVE/WiredTiger.wt.CORRUPT

test_wt4156_metadata_salvage: FAILED: main/440: WIFSIGNALED(status) == false

process aborting 

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