Log Cassandra keyspace name used in tests
Require explicit partitioning for part vert labels

Adding a precondition for #706, plus test coverage and some logging
tweaks.  TitanPartitionGraphTest now has tests in both the
OrderedKeyValueStore category (Cassandra BOP, HBase) and the
UnorderedKeyValueStore category (Cassandra Murmur3, RP).  There's a
new test method that checks that addVertexWithLabel fails when the
label is partitioned and explicit cluster partitioning is disabled.
There is also a pair of methods that check whether Titan correctly
guesses whether partitioning should be enabled/disabled based on the
backend StoreFeatures.
Merge branch 'titan05' of github.com:thinkaurelius/titan into titan05