METRON-1512 Refactor CONFIG_GET/CONFIG_PUT to Use ZKConfigurationsCache

[nickwallen]

NOTE: This depends on #982 and should not be merged until #982.

Currently the ConfigurationFunctions like CONFIG_GET and CONFIG_PUT use their own Zookeeper caching implementation. We have since implemented a reusable cache implementation ZkConfigurationsCache. These functions should use it.

Changes

1. The ConfigurationsFunctions now uses ZkConfigurationsCache.

2. There are now additional unit tests covering these functions.

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