KCC: raise KCCError, not Exception, in multiple places

KCC: raise KCCError, not Exception, in multiple places

"except Exception" lines will still catch them, but more fine-grained
control is possible.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>