Add sleep to TimeInactiveMicrosShouldBeSetUponUnstashAndStash in session_test

This test works by using a real clock and expecting it to advance after setting a transaction inactive. However on some platforms, it is possible for the clock to not advance at least one time quantum before checking the timer, so it fails. In master and 4.2 this is fixed using an injectable ticksource. This isn't available in 4.0, so we need to add a sleep.