Fix test in CachingStoreClientFactoryTest
Move KeySamplerCLI and KeyVersionFetcherCLI to tools package
fix NPE thrown on getAll requests with single key
Incorporating code review comments for changes in R2Store
Move to tusk-0.0.2 version
Update build.properties and release_notes for version 1.6.9
Adding BDB5 instructions
Refactor schema backward compatibility check

1. Fix a bug that will leave a store created even when exception has been thrown
2. Consolidate strings used by tests
3. Consolidate backward compatiblity check into StoreDefinitionUtils