Include auth credentials in 'info vnc' ("Daniel P. Berrange")

Include auth credentials in 'info vnc' ("Daniel P. Berrange")

This patch extends the 'info vnc' monitor output to include information
about the VNC client authentication credentials.

For clients authenticated using SASL, this will output the username.

For clients authenticated using x509 certificates, this will output
the x509 distinguished name.

Auth can be stacked, so both username & x509 dname may be shown.

    Server:
         address: 0.0.0.0:5902
            auth: vencrypt+x509+sasl
    Client:
         address: 10.33.6.67:38621
      x509 dname: C=GB,O=ACME,L=London,ST=London,CN=localhost
        username: admin
    Client:
         address: 10.33.6.63:38620
      x509 dname: C=GB,O=ACME,L=London,ST=London,CN=localhost
        username: admin

(cherry picked from commit 1263b7d6131cdaed2c460cf03757aaaf5696ec47)

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>