mysql: ignore slow log tables

We're running into issues with those, and they're completely
unnecessary.
Confirmed that non-existing tables can be ignored safely.
lib/cryo.rb: behave when a report isn't requested
bump version to 0.1.6
Merge pull request #10 from airbnb/pierre/ignore_slow_log

v0.1.6: do not require reporting, ignore slow_log{,_backup} tables