[RFR] 8160768: Add capability to custom resolve host/domain names within the default JDNI LDAP provider

[Rob McKenna]

As this enhancement is limited to JDK10 this frees us up to explore a
different approach.

http://cr.openjdk.java.net/~robm/8160768/webrev.06/

In this webrev we're using the Service Provider Interface to load an
implementation of the new LdapDnsProvider class. Implementations of this
class are responsible for resolving DNS endpoints for a given ldap url
should the default implementation be insufficient in a particular
environment.

Note: if a security manager is installed the ldapDnsProvider
RuntimePermission must be granted.

    -Rob