Current Ceph volume manager code doesn't take the builtin
kernel module into the account, so the `modinfo` will fail
in this case. Also, we need to add error handling code to
make sure the volume manager does work when proceeding to
continue, otherwise we will encounter the `rbd` related issue
in the following step even we have an artificial `agent` pod
in running state.
Signed-off-by: Dennis Chen <dennis.chen@arm.com>