Add a setup_mdv() method
Add a setup_mdv() method

There are several contexts in which we need to setup mdvs, so we should
abstract them.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,trgill/stratisd,mulkieran/stratisd,trgill/stratisd,mulkieran/stratisd,stratis-storage/stratisd,stratis-storage/stratisd