cephadm/tests: add initial test coverage for call function

cephadm/tests: add initial test coverage for call function

The call function provides the ability to run subprocesses, log output,
and provides an optional timeout parameter. This timeout parameter does
not appear to function correctly today, so we make use of
pytest.param/pytest.mark.xfail to mark these cases as already known to
fail.

Signed-off-by: John Mulligan <jmulligan@redhat.com>
(cherry picked from commit 471a017ad86f752f862d6211faa5231567ba78d8)