Fix default TTL for metadata cleaner

It seems to have been set to 3500 in a previous commit for debugging,
but it should be off by default
Fix one unit test that was not setting spark.cleaner.ttl
Merge pull request #381 from mateiz/default-ttl

Fix default TTL for metadata cleaner

It seems to have been set to 3500 in a previous commit for debugging, but it should be off by default.