rpc: implement server.manage-gids for group resolving on the bricks

The new volume option 'server.manage-gids' can be enabled in
environments where a user belongs to more than the current absolute
maximum of 93 groups. This option triggers the following behavior:

1. The AUTH_GLUSTERFS structure sent by GlusterFS clients (fuse, nfs or
   libgfapi) will contain only one (1) auxiliary group, instead of
   a full list. This reduces network usage and prevents problems in
   encoding the AUTH_GLUSTERFS structure which should fit in 400 bytes.
2. The single group in the RPC Calls received by the server is replaced
   by resolving the groups server-side. Permission checks and similar in
   lower xlators are applied against the full list of groups where the
   user belongs to, and not the single auxiliary group that the client
   sent.

Cherry picked from commit 2fd499d148fc8865c77de8b2c73fe0b7e1737882:
> BUG: 1053579
> Signed-off-by: Niels de Vos <ndevos@redhat.com>
> Reviewed-on: http://review.gluster.org/7501
> Tested-by: Gluster Build System <jenkins@build.gluster.com>
> Reviewed-by: Santosh Pradhan <spradhan@redhat.com>
> Reviewed-by: Harshavardhana <harsha@harshavardhana.net>
> Reviewed-by: Anand Avati <avati@redhat.com>

Change-Id: I9e540de13e3022f8b63ff893ecba511129a47b91
BUG: 1096425
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/7830
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Santosh Pradhan <spradhan@redhat.com>