javatunnel: add certificate chain to subject

Failing XACML authentication through the gsidcap door.

The issue is that XACML, being both an auth and map plugin, requires the full certificate chain to be in the Subject.  The gsi tunnel was only adding a GlobusPrincipal and an FQANPrincipal to the subject.

The tunnel now extracts the chain from the GSSCredential object and places it in the public credentials set of the subject.

Testing:

Before the patch, the XACML plugin would fail because it had incomplete information and which it processed in a faulty manner.  The error resulted from a mapping like the following:

[DCap-gsi-00-fndca4a-/DC=com/DC=DigiCert-Grid/O=Open Science
Grid/OU=People/CN=Kenneth Herner 1385-133 Login AUTH xacml] mapping
service
https://gums.fnal.gov:8443/gums/services/GUMSXACMLAuthorizationServicePort
returned localId LocalId[] for VomsExtensions[X509Subject='/fermilab',
X509SubjectIssuer='null', fqan='null', primary=false, VO='null',
VOMSSubject='null', VOMSSubjectIssuer='null']

After the patch, the dccp operation succeeds.

Target: master
Request: 2.6
Request: 2.2
Patch: http://rb.dcache.org/r/6112/
Require-book: no
Require-notes: yes
Acked-by: Tigran

RELEASE NOTES:
Fixes a bug whereby a combination of gsidcap with a VOMS cert and XACML authentication/mapping failed to authorize the user.