manifests/instance: don't concat_merge config hashes, just merge
manifests/instance: don't concat_merge config hashes, just merge

Although concat_merge provides advanced functionality, the existing
implementation does not concatenate arrays and so introduces some odd
behavior for existing configs. This can be re-enabled later, but as it
stands, consistency with existing behavior should ease the transition to
fully-qualified configs.

tylerjl/puppet-elasticsearch,tylerjl/puppet-elasticsearch,tylerjl/puppet-elasticsearch