Update appdirs to 1.4.3
Update appdirs to 1.4.3

Currently lower-constraint job fails due to changes in appdir's latest
version not included in the lower-constraints.
This patch updates the same.

Change-Id: I94a2e6c7300811aea3f41a79894f74a3bd25e9fc

mahak/neutron,openstack/neutron,openstack/neutron,openstack/neutron,mahak/neutron,mahak/neutron