ceph-volume: refactor strategies for explicit device arguments

ceph-volume: refactor strategies for explicit device arguments

This commit refactors lvm strategies to:
a) change the constructor to receive usage specific device lists
b) add classmethod with_auto_devices of automatic splitting by the
rotational flag (keep backwards compatible behavior)
c) rename ssds and hdds member variables to wal_devs and block_devs
d) add db_devs member variable

Signed-off-by: Jan Fajerski <jfajerski@suse.com>