Update appdirs lower constraint
Update appdirs lower constraint

The appdirs lower constraint of 1.3.0 does not work with isort >=
4.3.5, which references appdirs.system, which wasn't added until
appdirs 1.4.0. Neutron addressed this by increasing the lower
constraint to 1.4.3 [1] so we'll do the same.

[1] 9bfe63cf0786176cd48943d902690198e02fdb70

Change-Id: I5ba07e5504fe786bc7dcb42ef0f43034d5384f6f

stackforge/neutron-powervm,stackforge/neutron-powervm,openstack/networking-powervm,openstack/networking-powervm