Fix two issues with serializing non-compound range tombstones as
compound: convert a non-compound clustering element to compound and
actually advertise the issue to other nodes.
* git@github.com:duarten/scylla.git rt-compact-fixes/v1:
compound_compact: Allow rvalues in size()
sstables/sstables: Convert non-compound clustering element to compound
tests/sstable_mutation_test: Verify we can write/read non-correct RTs
service/storage_service: Export non-compound RT feature
(cherry picked from commit e9cce59b85)
740fcc73b8