Force wait for launcher to be ready after removing all tasks

In some cases (e.g. cuttlefish), launcher takes some time to initiate and we end up trying to continue the test (e.g. set a rotation) before `wm_on_create_called`, causing the test to flake

Fixes: 316500406
Test: atest WMShellFlickerServicePlatinumTests
Change-Id: Ie1c4c88749ed7e25385d1defae2dd18051176137
1 file changed