This adds basic coverage to IO threads by running the cluster and few selected Redis test suite tests with the IO threads enabled.
Also provides some necessary additional improvements to the test suite:
* Add --config to sentinel/cluster tests for arbitrary configuration.
* Fix --tags whitelisting which was broken.
* Add a `network` tag to some tests that are more network intensive. This is work in progress and more tests should be properly tagged in the future.
Add tests to check basic functionality of this optional keyword, and also tested with
a module (redisgraph). Checked quickly with valgrind, no issues.
Copies name the type name canonicalisation code from `typeCommand`, perhaps this would
be better factored out to prevent the two diverging and both needing to be edited to
add new `OBJ_*` types, but this is a little fiddly with C strings.
The [redis-doc](https://github.com/antirez/redis-doc/blob/master/commands.json) repo
will need to be updated with this new arg if accepted.
A quirk to be aware of here is that the GEO commands are backed by zsets not their own
type, so they're not distinguishable from other zsets.
Additionally, for sparse types this has the same behaviour as `MATCH` in that it may
return many empty results before giving something, even for large `COUNT`s.
Removing the fix about 50% of the times the test will not be able to
pass cleanly. It's very hard to write a test that will always fail, or
actually, it is possible but then it's likely that it will consistently
pass if we change some random bit, so better to use randomization here.
