encryption/crypt: Don't perform open on symlinks

Change-Id: I9be8634f8f3b09def21ba977050330aa3f26c230
BUG: 1099858
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7824
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>