Fix: sbd-inquisitor: tolerate and strip any leading spaces of command line option values

Somehow an user's own monitoring agent doesn't well parse an SBD_DEVICE
setting with spaces between the device names:

SBD_DEVICE="/dev/<a>; /dev/<b>; /dev/<c>"

And eventually it calls an sbd command:

sbd list -d " /dev/<b>"

• A space is prefixed to the device name which is quoted.

Of course it could be easily fixed in the setting or their agent. But
OTOH, sbd'd better tolerate and strip any leading spaces of command line
option values.