Merge branch 'sh-rescue-krb5-load-errors' into 'master'

Avoid requiring krb5 in migration to simplify source installs

Closes #7980

See merge request gitlab-org/gitlab-ee!7956

ee/db/migrate/20151113115819_canonicalize_kerberos_identities.rb

@@ -12,7 +12,7 @@ class CanonicalizeKerberosIdentities < ActiveRecord::Migration
       default_realm = krb5.get_default_realm
       krb5.close # release memory allocated by the krb5 library
       default_realm || ''
-    rescue StandardError
+    rescue StandardError, LoadError
       '' # could not find the system's default realm, maybe there's no Kerberos at all
     end
   end