syncop: set credentials of running process in @frame

Inherit the pid/euid/egid/groups of the running process in the
frame. Do this only in cases where a loaded frame was not
presented to the synctask.

This behavior is required for Samba VFS.

Change-Id: Ib181c90f47c6741197b9ce9f67a19e2914b647d2
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5153
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>