USS : fill proper uid and gid during a access call from nfs

Problem : when an user tries to access a file/folder for which
he does not have a proper permission required then fuse gives out
a proper error "Permission denied", but nfs does not give out that
error, rather he can access the file/folder. The reason being uid and
gid of call frame stack takes a default value of uid and gid which
point to root permission.

Solution : Set a proper uid and gid during a access call from nfs

Change-Id: Ib060706fde66ec7e60f242fab1f3e59122ed2245
BUG: 1167580
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/9194
Reviewed-by: Vijaikumar Mallikarjuna <vmallika@redhat.com>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>