winbindd: Add a cache of the samr and lsa handles for the passdb domain

winbindd: Add a cache of the samr and lsa handles for the passdb domain

This domain is very close, in AD DC configurations over a internal ncacn_np pipe
and otherwise in the same process via C linking.  It is however very expensive
to re-create the binding handle per SID->name lookup, so keep a cache.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>