ISPN-263 Handle cluster partitions

https://issues.jboss.org/browse/ISPN-263

I added one more commit with some test fixes.
Actually it looks like a node receiving a command with `missingData = true` will enter unavailable mode, not degraded mode, so I'm renaming `CacheTopology.degradedMode` to `isMissingData`. I'm still not very sure on when we should enter unavailable mode and when degraded mode, so I need to follow up on this for Beta2.