Allow temporary databases in sqlite driver

http://www3.sqlite.org/inmemorydb.html#temp_db
[ChangeLog][QtSql][QSQLITE] Enable creating temporary databases

Change-Id: I9972fba5c91eca55cfc5a84f94cff03d19992324
Reviewed-by: Tobias Koenig <tobias.koenig.qnx@kdab.com>
Reviewed-by: Mark Brand <mabrand@mabrand.nl>