util: remove use hardcoded DMIDECODE path

util: remove use hardcoded DMIDECODE path

Allow virCommand to find 'dmidecode' in $PATH. This command is only
usable when running privileged since it relies on reading from a
privileged kernel file. Thus we can assume both 'bin' and 'sbin' dirs
will be in $PATH and virFindFileInPath will do the right thing to
find it when called by virCommand.

Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>