Attempt to fix a failure in test case innodb.innodb_information_schema seen occasionally in Buildbot.

The test case waits for other threads to complete, but the wait is only 2
seconds. This is likely to sometimes be too little on our heavily loaded
buildbot VMs, that can easily stall for more than 2 seconds from time to time.

So let's try to increase the timeout (to about 40 seconds) and see if it
helps.