build: remove /sbin/ldconfig as interpreter

using /sbin/ldconfig as interpreter in pre/post/postun throws error
/sbin/ldconfig: relative path `1' used to build cache

BUG: 1145989
Change-Id: Ic321f200d92d2e49ff797965a006f63f483d29be
Signed-off-by: Bala.FA <barumuga@redhat.com>
Reviewed-on: http://review.gluster.org/8835
Reviewed-by: Lalatendu Mohanty <lmohanty@redhat.com>
Tested-by: Lalatendu Mohanty <lmohanty@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>