Run integration tests against cassandra 2.0

- Add profile to set cassandra maven plugin version to 2.0
- Run integration tests against cassandra 2.0 by default since that is
  what we will be running in the new prod environment.
Remove openjdk6 from travis test matrix

the cassandra 2.0 maven crashes when run against java 6.
add IMetricWriter interface
add support for (de)serialization of both implementations of IMetric
Merge pull request #284 from fourk/add_imetric_writer

add IMetricWriter interface
Configure RiemannReporter prefix

We have a configuration option in BF to configure the RiemannReporter
prefix, but don't use it. Correcting that oversight...
Merge pull request #286 from dlobue/configure_riemann_prefix

Configure RiemannReporter prefix
log the serialized text on assertion failure
enforce ordering of json properties
Merge pull request #273 from dlobue/cassandra_2.0_integration_tests

Run integration tests against cassandra 2.0
Merge pull request #285 from fourk/serdes_support_for_imetric

add support for (de)serialization of both implementations of IMetric
stubbed in drop wizard ingestion.
a little bit of cleanup.
Ingest raw metrics.

* FakeMetricsWriter so that writes are a noop. Specified in IngestConfiguration.
* Plumb IMetricsWriter and ScheduleContext into BasicIngestResource and Application.
* Add optional units field to BasicMetric.
Immutable response for basic ingest
Ingest support for aggregated metrics (including multi-tenant)
fix aggregated bugs:

* gauge was declaring a duplicate json field.
* percentile definition did not match expected data
Add a readme
port over a few more properties from the default blueflood configuration.
Wire up shard state management.