block manager object race

Evergreen has been failing recently due to the failure of test_bug010.test_bug010.test_checkpoint_dirty.

The following is the error generated by the assertion that aborts the test.

[1499472754:854048][91694:0x7fffad1053c0], test_bug010.test_bug010.test_checkpoint_dirty, file:test_bug010798.wt, WT_SESSION.open_cursor: src/block/block_ckpt.c, 93: block->live_open == false

[1499472754:902935][91694:0x7fffad1053c0], test_bug010.test_bug010.test_checkpoint_dirty, file:test_bug010798.wt, WT_SESSION.open_cursor: aborting WiredTiger library

This issue was first reported testing the merge of WT-3403 (4738239eb7), but the last reported success was with the merge of WT-3401 and there are un-tested commits between the two.

Running this on my Linux machine and on my OSX laptop for 100 runs each was unable to reproduce the issue