Server Upgrade: raise RuntimeError instead exit()

Ldapupdater should not call sys.exit() in the middle of execution and
should fail gracefully

https://fedorahosted.org/freeipa/ticket/4904

Reviewed-By: David Kupka <dkupka@redhat.com>

ipaserver/install/ldapupdate.py

@@ -894,7 +894,7 @@ class LDAPUpdate:
                     data = self.read_file(f)
                 except Exception, e:
                     self.error("error reading update file '%s'", f)
-                    sys.exit(e)
+                    raise RuntimeError(e)
 
                 self.parse_update_file(f, data, all_updates)
                 self._run_updates(all_updates)