[no-release-notes] enginetest harness changes to more closely match running server

[zachmu]

This change rewrites the DoltHarness to use an engine.SqlEngine, which makes its behavior more closely match what happens in a running server.

[coffeegoddd]

@zachmu DOLT

read_tests	from_latency	to_latency	percent_change
covering_index_scan	0.54	0.54	0.0
groupby_scan	9.91	9.91	0.0
index_join	1.89	1.86	-1.59
index_join_scan	1.34	1.34	0.0
index_scan	21.89	21.89	0.0
oltp_point_select	0.26	0.26	0.0
oltp_read_only	5.09	5.09	0.0
select_random_points	0.51	0.51	0.0
select_random_ranges	0.57	0.57	0.0
table_scan	21.89	21.89	0.0
types_table_scan	66.84	69.29	3.67

write_tests	from_latency	to_latency	percent_change
oltp_delete_insert	6.32	6.43	1.74
oltp_insert	3.13	3.13	0.0
oltp_read_write	11.24	11.24	0.0
oltp_update_index	3.25	3.19	-1.85
oltp_update_non_index	3.07	3.07	0.0
oltp_write_only	5.99	6.09	1.67
types_delete_insert	6.91	6.91	0.0

[coffeegoddd]

@zachmu DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
0f54707	ok	5937471

version	total_tests
0f54707	5937471

correctness_percentage
100.0

[coffeegoddd]

@zachmu DOLT

test_name	from_latency_p95	to_latency_p95	percent_change
tpcc-scale-factor-1	53.85	53.85	0.0

test_name	from_server_name	from_server_version	from_tps	to_server_name	to_server_version	to_tps	percent_change
tpcc-scale-factor-1	dolt	e3a6968	45.05	dolt	0f54707	44.31	-1.64