ci: Use libcap-ng

ci: Use libcap-ng

We currently enable libcap-dev in build-clang to pick up the 9p proxy
helper.  Paolo's patch changes (commit 7e46261368d1) that to use
libcap-ng, so switch to using it.  This also means we'll be testing the
scsi pr manager and the bridge helper.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[groug, mention SHA1 that dropped libcap]
Signed-off-by: Greg Kurz <groug@kaod.org>