Bucketing: Make CLUSTERED BY do CLUSTER BY if no explicit sorting is specified

The user's expectation of

"create external table bucketed (key int) clustered by (key) into 4 buckets stored as orc;"

is that the table will cluster the key into 4 buckets, while the file layout does not do any actual clustering of rows.

In the absence of a "SORTED BY", this can automatically do a "SORTED BY (key)" to cluster the keys within the file as expected.