test/pybind/test_ceph_argparse: add a test where args contains comma

test/pybind/test_ceph_argparse: add a test where args contains comma

to ensure the support for the new syntax of "prefix --name bon,jour"
does not break existing behavior of "prefix hello cruel,world" where value2
contains reads "hello,world", and the parsed result should be

prefix="prefix"
value=["hello", "cruel,world"]

instead of something like

prefix="prefix"
value=["hello", "cruel", "world"]

or

prefix="prefix"
value=["cruel", "world"]

the above test only applies to the test where "value" is a CephString.
if "value" is a CephChoices, the parsed argument should be

prefix="prefix"
value=["hello", "cruel", "world"]

Signed-off-by: Kefu Chai <kchai@redhat.com>