Rework ceph-disk to use LUKS for encrypted partitions

LUKS allows for validation of the key at mount time (rather than
simply mounting a random partition), specification of the encryption
parameters in the header and key rollover of the slot key (the one
that needs to be stored).

New parameters 'osd cryptsetup parameters' and 'osd dmcrypt key size' are
added.  These allow these important policy choices to be overridden or
kept consistent per-site.

The previous default, plain mode (rather than using LUKS) is available
by setting 'osd dmcrypt type = plain'

Signed-off-by: Andrew Bartlett <abartlet@catalyst.net.nz>