Fix for 1318788 - Create salt table keyed on interval columns generates
core

When creating column desc the leading precision for the interval
datatype  is not being set correctly. Comments from definition of struct
ComTdbVirtTableTableInfo in ComTdb.h inidcate that for interval type the
leading precision should be the precision.

Change-Id: I2aa7da5f5ba3bbef084b5180125c2fe99195a2ed