Don't assume test user has ID 1 in SpecialPageTest

SpecialPageTest seems to assume
the first database user has ID number 1.

In case of the current PostgreSQL test
setup it does not have to be the case.

This query:

Query pgtest01 (101) (slave):
SELECT /* User::loadFromDatabase 127.0.0.1
*/  user_id /* more fields */ FROM "unittest_mwuser"
WHERE user_id = '1'  LIMIT 1

fails, because UTSysop has been added by the
test setup before with some other ID:

Query pgtest01 (65) (slave):

INSERT /* User::addToDatabase 127.0.0.1 */
INTO "unittest _mwuser"
	(user_id,user_name /* more fields */
VALUES ('322','UTSysop' /* more values */

Change-Id: I7b0a6a9001765111669051d57e675e588b71ba17
Merge "Don't assume test user has ID 1 in SpecialPageTest"