EX-4333 sec: traces for supplementary groups handling

EX-4333 sec: traces for supplementary groups handling

Add traces in the code to ease understanding of supplementary groups
handling, in particular for the INTERNAL identity_upcall.

Change-Id: I4b2298cf5c3b400e7a1436384653ce01a462a2e0
Test-Parameters: trivial
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-on: https://review.whamcloud.com/47697
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>