capabilites: introduce new has_ns_capabilities_noaudit

For consistency in interfaces, introduce a new interface called
has_ns_capabilities_noaudit.  It checks if the given task has the given
capability in the given namespace.  Use this new function by
has_capabilities_noaudit.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>