The lookaside file isn't widely testing in our Python functional test suite. We should construct more Python test cases that trigger lookaside file usage, and confirm correctness. The specific cases that trigger lookaside file usage are:

• Updates are pinned in cache by old readers, by old timestamp, or old snapshot
• The cache is full

It would be good to add coverage that:

• Ensures the lookaside file is used when required.
• Ensures that content written to the lookaside file can be read (i.e: the expected version of data is used)
• Ensures that the lookaside file doesn't interfere with durability in any way (i.e: restarting WiredTiger always clears the content of the lookaside file.