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Fixing a deprecation warning in FS dataset test.

Should use the Iterator API rather than read().
CDK-139: Adding location to DatasetDescriptors.

This adds a location URL to the DatasetDescriptor, which is accessible
through getLocation(). This also adds location(String) and location(URI)
and hasLocation() methods to the Builder and changes the schema(String)
to be a URI rather than a schema literal. To set a schema literal from a
String, schemaLiteral(String) was added.
CDK-139: Adding Configuration to DatasetDescriptor.

The last commit's addition of an optional location to the
DatasetDescriptor enables the MetadataProvider to determine the location
of Datasets and pass that location to a DatasetRepository. But, the
repository implementation was still dependent on having the correct
FileSystem. Adding the Configuration to the DatasetDescriptor as well
allows the FileSystemDatasetRepository to construct the correct
FileSystem for a descriptor, from the location URI and the
Configuration.
CDK-139: Adding list method to MetadataProvider.

If the DatasetRepository no longer determines the locations of data
sets, and instead relies on getting the location from the
MetadataProvider, then the repository can't list the available data
sets. The MetadataProvider determines what data sets are available, so
it should have the list() method. This is also mroe consistent with the
Hive implementation, where the repository already delegated to the
MetadataProvider.

The DatasetRepository interface still has exists and list methods, but
these should delegate to the MetadataProvider unless they need to be
hooked. For instance, if a Dataset has metadata but has not yet been
written to.
CDK-139: Updating FS impl to use Descr locations.

Now that DatasetDescriptors have getLocation and getConfiguration, the
FileSystem Dataset/Repo/Provider implementations can use the Descriptor
to pass Dataset paths. Now, the FileSystemMetadataProvider assigns a
location when creating a Dataset. FileSystemDatasetRepository uses the
paths that are set on the DatasetDescriptor.

Because location and configuration are being passed by the
DatasetDescriptor, all of the classes necessary to get a FileSystem and
Path for a FS-based Dataset are available. So this commit also removes
the FileSystem and root Path from the FS repo and the FileSystem option
from the FileSystemDataset.Builder. This makes the FS classes more
flexible and handles Configurations more cleanly: only the
MetadataProvider is instantiated with a Configuration, which is passed
via Immutable objects where it needs to go.

Several helper methods that were previously protected because they were
shared between the FS MetadataProvider and DatasetRepository are now
private and owned by the MetadataProvider.

Tests are up-to-date and passing for core, but this breaks the Hive
integration. This update is primarily to fix problems in the Hive
integration anyway.
CDK-139: Separating common tests out of FS.

This extracts tests that should pass on all DatasetRepository
implementations into the TestDatasetRepositories set. The FS tests now
inherit from this add add other tests, like making sure that the data
directory exists after a dataset is created. Minor updates to the FS
repository are included where tests found bugs.

A major update to the FS repository and common tests is the new
MemoryMetadataProvider, which is a simple provider with no durability
intended for testing. Both the common and FS tests use this provider
rather than the FS provider. MemoryMetadataProvider is tested by
TestMemoryMetadataProvider, which inherits from the new common set,
TestMetadataProviders.

The common tests include checks that verify IllegalArgumentException is
thrown, which has been added to the API documentation in the interface.
Similar additions haven't been made to the FS MetadataProvider yet.
Cleaning up DatasetReader tests.

Clean up to match the recent repo and provider tests
* Renamed TestDatasetReaderCommon to TestDatasetReaders
* Merged Test...DatasetReaderCommon and Test...DatasetReader classes