conf: Introduce TLS options for VxHS block device clients

conf: Introduce TLS options for VxHS block device clients

Add a new TLS X.509 certificate type - "vxhs". This will handle the
creation of a TLS certificate capability for properly configured
VxHS network block device clients.

The following describes the behavior of TLS for VxHS block device:

  (1) Two new options have been added in /etc/libvirt/qemu.conf
      to control TLS behavior with VxHS block devices
      "vxhs_tls" and "vxhs_tls_x509_cert_dir".
  (2) Setting "vxhs_tls=1" in /etc/libvirt/qemu.conf will enable
      TLS for VxHS block devices.
  (3) "vxhs_tls_x509_cert_dir" can be set to the full path where the
      TLS CA certificate and the client certificate and keys are saved.
      If this value is missing, the "default_tls_x509_cert_dir" will be
      used instead. If the environment is not configured properly the
      authentication to the VxHS server will fail.

Signed-off-by: Ashish Mittal <Ashish.Mittal@veritas.com>
Signed-off-by: John Ferlan <jferlan@redhat.com>