Need tests for different configurations of buffer_alignment and direct_io

It would be good to have tests for different values of buffer_alignment. Alignment is used in sizing data file and log file writes. There is some interaction between buffer_alignment and the values of direct_io, so any tests may have to change both. The Python test suite currently has no tests that use buffer_alignment or direct_io.

This came up in the review for WT-4199. Although it's not strictly tied to that ticket, it would have improved that testing.