[SPARK-2817] [SQL] add "show create table" support

In spark sql component, the "show create table" syntax had been disabled.
We thought it is a useful funciton to describe a hive table.
in repo tests is checking to see if the tests are there or if we should look for them in the hive distribution (they weren't always bundled with the source tree).  If we need a temporary directory, we should use the mechanisms provided by the JVM for that (`File.createTempFile`)