Fix flaky RoR test when running on cloud devices

The failure mostly happens on remote cuttlefish instance. And the
reason of the flakiness is likely the network delay, causing the
UI automation to enter the key pad before the lock screen shows
up. Add a delay to make sure the lock screen shows up.

Bug: 189853309
Test: lunch a remote cf, atest CtsAppSecurityHostTestCases:android.appsecurity.cts.ResumeOnRebootHostTest
Change-Id: Iff640f5c8517fb5cd586946ab69331e10a1da62f
Merged-In: Iff640f5c8517fb5cd586946ab69331e10a1da62f
(cherry picked from commit df88e58c0760f13dbb35459230ae868fab16df44)