DbusContext::get_next_id() doesn't need to take a mutable self.
DbusContext::get_next_id() doesn't need to take a mutable self.

Remove that requirement, and remove the need to clone the
dbus_context in a few places.

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

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