Handle interface names containing "." or "-"

This fixes https://bugzilla.redhat.com/show_bug.cgi?id=1057938 for
packstack by calling regsubst() to replace "." or "-" with "_" in interface
names when looking up ipaddress_* facts.

(Update for "-" based on comment in https://github.com/redhat-openstack/astapor/pull/111).