parsertest now destroy virtual table under SQLite

parsertest now destroy virtual table under SQLite

Fix:
Bug 29912 - Unit tests break if parsertest tables are still present

The parserTest suite duplicate available tables. When using temporary table
it assumed every table are temporary. Under SQLite searchindex is a virtual
table and thus remained after a run of parserTests.php
As a side effect, when running the PHPUnit with that remaining table, it
caused a nice error:

The last attempted database query was:
"DELETE FROM unittest_parsertest_searchindex"
from within function "MediaWikiTestCase::resetDB".
Database returned error "1: SQL logic error or missing database"

This patch is not needed for REL1_18 continuous integration since we
never run the parserTests.php script.