implemented metric validation prior to storing
make validate a method on the metricBatch
review comments fixed and fixed unit tests
return errors.trace instead of bare err
Merge pull request #1074 from mattyw/metric-state-server-validation

implemented metric validation prior to storing

Before metrics are stored we do a validation check.  Validity is defined by the charm package - This pr just adds the call to the state server. The metrics tests have been updated to check the failure modes of validation and existing tests have been updated to ensure they use valid data

http://reviews.vapour.ws/r/376/