extras/hookscripts: Add default logfile for glusterfs vfs plugin.

Glusterfs vfs plugin for samba makes call into gfapi which brings
up complete client process stack of gluster. Not having default
log file means not logging client process at all.

This patch adds default logfile and loglevel for vfs plugin.

Change-Id: Ie0fb6bbb445d6f3349fc35c713743094c0f08915
BUG: 999910
Signed-off-by: Raghavendra Talur <rtalur@redhat.com>
Reviewed-on: http://review.gluster.org/5685
Reviewed-by: Anand Avati <avati@redhat.com>
Tested-by: Anand Avati <avati@redhat.com>