bootstat: fix test regression (exec_background)

Deal with regression from 557a9d4054
where bootstat was moved to exec_background and actions delayed
to improve boot time.  Add a 1 second sleep rather than trying to
inspect the dmesg (debug only) for clues to the end of bootstat.

Test: system/core/bootstat/boot_reason_test.sh
Bug: 63736262
Change-Id: I87dfb6a07130112bf51c367632967efa53ea2534

bootstat/boot_reason_test.sh

@@ -194,10 +194,12 @@ wait_for_screen() {
               sed -n 's/[[]sys[.]\(boot_completed\|logbootcomplete\)[]]: [[]\([01]\)[]]$/\1=\2/p'`
         if [ "${vals}" = "`echo boot_completed=1 ; echo logbootcomplete=1`" ]
         then
+          sleep 1
           break
         fi
         if [ "${vals}" = "`echo logbootcomplete=1 ; echo boot_completed=1`" ]
         then
+          sleep 1
           break
         fi
       fi