roles: bootstrap-os: Use 'hostname' command on Tumbleweed

openSUSE Tumbleweed is having the same problems with CoreOS when it
comes to using the hostname ansible module (#1588, #1600) so we need
to apply a similar workaround.

Co-authored-by: Markos Chandras <mchandras@suse.de>
Link: http://bugzilla.opensuse.org/show_bug.cgi?id=997614