common/util: do not print error if VERSION_ID is missing

per os-release(5), VERSION_ID is optional.

Fixes: http://tracker.ceph.com/issues/23477
Signed-off-by: Kefu Chai <kchai@redhat.com>
(cherry picked from commit eff4961)

src/common/util.cc

@@ -182,7 +182,7 @@ static void distro_detect(map<string, string> *m, CephContext *cct)
     lderr(cct) << "distro_detect - /etc/os-release is required" << dendl;
   }
 
-  for (const char* rk: {"distro", "distro_version"}) {
+  for (const char* rk: {"distro", "distro_description"}) {
     if (m->find(rk) == m->end())
       lderr(cct) << "distro_detect - can't detect " << rk << dendl;
   }