test/sun/security/krb5/config/dns.sh needs to re-examined or replaced

Changes for the modular image are currently accumulating in the jigsaw/m2 forest.

test/sun/security/krb5/config/dns.sh is failing in this forest with the following exception:

Exception in thread "main" java.lang.NoClassDefFoundError: com/sun/jndi/dns/DnsContext
at javax.naming.spi.NamingManager.getURLContext(NamingManager.java:46)
at sun.security.krb5.KrbServiceLocator.getKerberosService(KrbServiceLocator.java:141)
at sun.security.krb5.Config.getKDCFromDNS(Config.java:1220)
at sun.security.krb5.Config.getKDCList(Config.java:1106)
at DNS.main(DNS.java:32)

The issue is that this test is using -Xbootclasspath/p to replace NamingManager and have it return a hacked DnsContext. The main problem with this is the assumption that the JNDI DNS provider is loaded by the boot class path, but it is no longer the case as it changing to be loaded by the extensions class loader.

As part of re-examining this test then the use of -Xbootclasspath/p should be examined too as this will likely to away and be replaced with an alternative mechanism for overriding classes in modules that are linked into the image.