Use oslo-rootwrap in config directory names

Use oslo-rootwrap rather than oslo.rootwrap in directory names
(/etc/oslo-rootwrap and /usr/share/oslo-rootwrap), as suggested by
Chuck. Since this package is actually consumed through its binary
(oslo-rootwrap) rather than its library (oslo.rootwrap), this is
probably more appropriate.

Change-Id: I0e249d70937307b5fe116750923c20d487506c97