handle multiple NTP servers (bnc#895824)

stoney backport of https://github.com/crowbar/barclamp-provisioner/pull/345

sntp seems to use only the first NTP server and ignore others
https://bugzilla.novell.com/show_bug.cgi?id=895824

cherry picked from commit e2be9b05d90646e0a0681eb1b83f5b0baeb69786
Conflicts:
	chef/cookbooks/provisioner/templates/default/crowbar_join.suse.sh.erb