[Minor] [SQL] [SPARK-6729] Minor fix for DriverQuirks get

The function uses .substring(0, X), which will trigger OutOfBoundsException if string length is less than X. A better way to do this is to use startsWith, which won't error out in this case.

Author: Volodymyr Lyubinets <vlyubin@gmail.com>

Closes #5378 from vlyubin/quirks and squashes the following commits:

504e8e0 [Volodymyr Lyubinets] Minor fix for DriverQuirks get