Close backup database after sync and restore to release file descriptors

[elianddb]

On NFS, open file descriptors prevent the directory from being deleted, so dolt_backup remove would succeed but the backup directory could not be removed until the server was restarted. The same issue existed for dolt_backup restore on the source backup. Fixed by closing both databases with defer Close() after the operation completes.

[coffeegoddd]

@elianddb DOLT

read_tests	from_latency	to_latency	percent_change
covering_index_scan	0.55	0.55	0.0
groupby_scan	9.73	10.09	3.7
index_join	1.86	1.86	0.0
index_join_scan	1.42	1.42	0.0
index_scan	22.28	21.89	-1.75
oltp_point_select	0.27	0.27	0.0
oltp_read_only	5.28	5.28	0.0
select_random_points	0.54	0.54	0.0
select_random_ranges	0.56	0.55	-1.79
table_scan	22.28	21.89	-1.75
types_table_scan	66.84	66.84	0.0

write_tests	from_latency	to_latency	percent_change
oltp_delete_insert	6.32	6.32	0.0
oltp_insert	3.13	3.13	0.0
oltp_read_write	11.45	11.45	0.0
oltp_update_index	3.19	3.19	0.0
oltp_update_non_index	3.13	3.13	0.0
oltp_write_only	5.99	6.09	1.67
types_delete_insert	6.79	6.79	0.0

[coffeegoddd]

@elianddb DOLT

test_name	from_latency_p95	to_latency_p95	percent_change
tpcc-scale-factor-1	61.08	61.08	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	bf58103	37.72	dolt	a68d02a	38.22	1.33

[coffeegoddd]

@elianddb DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
a68d02a	ok	5937471

version	total_tests
a68d02a	5937471

correctness_percentage
100.0