MDEV-29993: myrocks_hotbackup.1 and test suite files installed when engine is disabled

storage/rocksdb/CMakeLists.txt

 # TODO: Copyrights
 
+IF(PLUGIN_ROCKSDB STREQUAL "NO")
+  ADD_FEATURE_INFO(ROCKSDB "OFF" "Storage Engine")
+  RETURN()
+ENDIF()
+
 SET(CPACK_RPM_rocksdb-engine_PACKAGE_SUMMARY "RocksDB storage engine for MariaDB server" PARENT_SCOPE)
 SET(CPACK_RPM_rocksdb-engine_PACKAGE_DESCRIPTION "The RocksDB storage engine is a high performance storage engine, aimed
 at maximising storage efficiency while maintaining InnoDB-like performance." PARENT_SCOPE)