fs_mgr: overlayfs: test: if wait_for_screen times out, skip later

To improve the test period for adb-remount-test.sh, if the device
fails to get to the launcher on the first try when wait_for_screen,
then print a warning to skip all later wait_for_screen conditions.

The wait_for_screen testing is really there to deal with first
confirming that the device is capable of getting to the launcher,
and that later tests that influence corners of adb remount behavior
do not result in a failure to get to the launcher screen.  The
developer should look into ways to fix the failure to get to the
launcher on the first try, but failure to do so should have no
bearing on the remaining tests, so dropping the wait_for_screen
functionality is not an issue.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Test: adb-remount-test.sh
Bug: 148881519
Change-Id: I5b4a87d6e1f545a304eb74f2114aadd1128f25b3