OPENDJ-813 (CR-1404) SNMP connection handler does not start when allowed-manager prop is set and server is running with JDK1.7

The issue here is that the TreeSet implementation changed starting from Java 1.7.
When adding as a first element a non Comparable object, Java 1.7 will now throw a ClassCastException.

SNMPInetAddressAcl.java:
Changed hostsList instance member type from TreeSet to Set + HashSet.
In checkReadPermission() used Set.contains().
Used foreach.