ceph crush osd set does not create a device if it does not exist

Introduced "ceph osd crush add" to add a device to the crush map if
it does not yet exist, before running "ceph osd crush set".

The behavior of "ceph osd crush set" changed in Ceph Emperor, it
will not create the device automatically if it does not exist anymore.
See release notes:
http://ceph.com/docs/master/release-notes/#v0-72-emperor

I've tested this fix on my own continuous integration setup and it
works well on both Dumpling and Emperor - I am currently unable to
test it against Cuttlefish but it should also work.