Use number of available cpu instead of total number of cpus in tests

test/test_functional/test_align-parser.py

test/test_functional/test_all-parser.py

test/test_functional/test_pangenome-parser.py

test/test_functional/test_prepare-parser.py

test/test_functional/test_tree-parser.py

test/test_unit/test_utils-argparse.py