Fixup strip trailing whitespaces for getuid return value

Fixup strip trailing whitespaces for getuid return value

The getuid callout might return a wwid with trailing
spaces (or containing only spaces). The existing
fixup code will only work if the getuid callout
returns a wwid with the entire space used up.
So fixup this and also update the logging output
to correctly state '<empty>' if the getuid was
found to be empty.

References: bnc#542085

Signed-off-by: Hannes Reinecke <hare@suse.de>