handle multiple NTP servers (bnc#895824)

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 8d6711d259d21a923134b0e0f5a02176de3d72b9
 (stoney branch)
Merge pull request #353 from SUSE-Cloud/release/roxy/master

handle multiple NTP servers (bnc#895824)