Prevent Removal of Realm when directory is not available at startup

When using JNDIRealm, if the ldap is not available at startup, the Realm is removed from configuration, which can lead to cryptic errors if there was only one realm configured. This can happen if tomcat is started before the ldap when it is patch day.

The idea here is to just log an error (maybe a warning would be better), and let the realm retry at a latter time.