Check number of devices added in init_cache method
Check number of devices added in init_cache method

We should do this for the same reason that we do it in add add_data_devices
or add_cache_devices.

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

stratis-storage/stratis-cli,stratis-storage/stratis-cli