Split long running tests
test_database_with_data_in_sstables_is_a_mutation_source_plain and
test_database_with_data_in_sstables_is_a_mutation_source_reverse.
They run with x_log2_compaction_groups of 0 and 1, each one taking from
10 to 15 minutes each in debug mode, for a total of 28 and 22 minutes.
Split the test cases to run with 0 and 1, so test.py can run them in
parallel.
Refs #13905
Signed-off-by: Alejo Sanchez <alejo.sanchez@scylladb.com>
Closes#14356
3cbfd863eb