misc: Fix get_wwn_id_map() to be optional

Not all plana nodes have symlinks setup when
we check /dev/disk/by-id/wwn-*.  Instead of failing
here, just use the /dev/disk/sd* devices.

Signed-off-by: Sam Lang <sam.lang@inktank.com>
nuke:  Optionally check console status

Only check the ipmi console status if the ipmi
parameters have been defined in .teuthology.yaml.

Signed-off-by: Sam Lang <sam.lang@inktank.com>