Add client library for SID related lookups
This patch add a library for client side lookups for a SID or with a
SID through the calls:
- sss_nss_getsidbyname
- sss_nss_getsidbyid
- sss_nss_getnamebysid
- sss_nss_getidbysid
The library is called libsss_nss_idmap and the contributed spec file
will create two new packages libsss_nss_idmap and
libsss_nss_idmap-devel.